/*
  Copyright (C) 2013 Ariya Hidayat <ariya.hidayat@gmail.com>
  Copyright (C) 2013 Thaddee Tyl <thaddee.tyl@gmail.com>
  Copyright (C) 2012 Ariya Hidayat <ariya.hidayat@gmail.com>
  Copyright (C) 2012 Mathias Bynens <mathias@qiwi.be>
  Copyright (C) 2012 Joost-Wim Boekesteijn <joost-wim@boekesteijn.nl>
  Copyright (C) 2012 Kris Kowal <kris.kowal@cixar.com>
  Copyright (C) 2012 Yusuke Suzuki <utatane.tea@gmail.com>
  Copyright (C) 2012 Arpad Borsos <arpad.borsos@googlemail.com>
  Copyright (C) 2011 Ariya Hidayat <ariya.hidayat@gmail.com>

  Redistribution and use in source and binary forms, with or without
  modification, are permitted provided that the following conditions are met:

    * Redistributions of source code must retain the above copyright
      notice, this list of conditions and the following disclaimer.
    * Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.

  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> BE LIABLE FOR ANY
  DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
  (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
  ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/

/*jslint bitwise:true plusplus:true */
/*global esprima:true, define:true, exports:true, window: true,
throwError: true, generateStatement: true, peek: true,
parseAssignmentExpression: true, parseBlock: true,
parseClassExpression: true, parseClassDeclaration: true, parseExpression: true,
parseForStatement: true,
parseFunctionDeclaration: true, parseFunctionExpression: true,
parseFunctionSourceElements: true, parseVariableIdentifier: true,
parseImportSpecifier: true,
parseLeftHandSideExpression: true, parseParams: true, validateParam: true,
parseSpreadOrAssignmentExpression: true,
parseStatement: true, parseSourceElement: true, parseConciseBody: true,
advanceXJSChild: true, isXJSIdentifierStart: true, isXJSIdentifierPart: true,
scanXJSStringLiteral: true, scanXJSIdentifier: true,
parseXJSAttributeValue: true, parseXJSChild: true, parseXJSElement: true, parseXJSExpressionContainer: true, parseXJSEmptyExpression: true,
parseTypeAnnotation: true, parseTypeAnnotatableIdentifier: true,
parseYieldExpression: true, parseAwaitExpression: true
*/

(function (root, factory) {
    'use strict';

    // Universal Module Definition (UMD) to support AMD, CommonJS/Node.js,
    // Rhino, and plain browser loading.
    if (typeof define === 'function' && define.amd) {
        define(['exports'], factory);
    } else if (typeof exports !== 'undefined') {
        factory(exports);
    } else {
        factory((root.esprima = {}));
    }
}(this, function (exports) {
    'use strict';

    var Token,
        TokenName,
        FnExprTokens,
        Syntax,
        PropertyKind,
        Messages,
        Regex,
        SyntaxTreeDelegate,
        XHTMLEntities,
        ClassPropertyType,
        source,
        strict,
        index,
        lineNumber,
        lineStart,
        length,
        delegate,
        lookahead,
        state,
        extra;

    Token = {
        BooleanLiteral: 1,
        EOF: 2,
        Identifier: 3,
        Keyword: 4,
        NullLiteral: 5,
        NumericLiteral: 6,
        Punctuator: 7,
        StringLiteral: 8,
        RegularExpression: 9,
        Template: 10,
        XJSIdentifier: 11,
        XJSText: 12
    };

    TokenName = {};
    TokenName[Token.BooleanLiteral] = 'Boolean';
    TokenName[Token.EOF] = '<end>';
    TokenName[Token.Identifier] = 'Identifier';
    TokenName[Token.Keyword] = 'Keyword';
    TokenName[Token.NullLiteral] = 'Null';
    TokenName[Token.NumericLiteral] = 'Numeric';
    TokenName[Token.Punctuator] = 'Punctuator';
    TokenName[Token.StringLiteral] = 'String';
    TokenName[Token.XJSIdentifier] = 'XJSIdentifier';
    TokenName[Token.XJSText] = 'XJSText';
    TokenName[Token.RegularExpression] = 'RegularExpression';

    // A function following one of those tokens is an expression.
    FnExprTokens = ['(', '{', '[', 'in', 'typeof', 'instanceof', 'new',
                    'return', 'case', 'delete', 'throw', 'void',
                    // assignment operators
                    '=', '+=', '-=', '*=', '/=', '%=', '<<=', '>>=', '>>>=',
                    '&=', '|=', '^=', ',',
                    // binary/unary operators
                    '+', '-', '*', '/', '%', '++', '--', '<<', '>>', '>>>', '&',
                    '|', '^', '!', '~', '&&', '||', '?', ':', '===', '==', '>=',
                    '<=', '<', '>', '!=', '!=='];

    Syntax = {
        ArrayExpression: 'ArrayExpression',
        ArrayPattern: 'ArrayPattern',
        ArrowFunctionExpression: 'ArrowFunctionExpression',
        AssignmentExpression: 'AssignmentExpression',
        BinaryExpression: 'BinaryExpression',
        BlockStatement: 'BlockStatement',
        BreakStatement: 'BreakStatement',
        CallExpression: 'CallExpression',
        CatchClause: 'CatchClause',
        ClassBody: 'ClassBody',
        ClassDeclaration: 'ClassDeclaration',
        ClassExpression: 'ClassExpression',
        ClassProperty: 'ClassProperty',
        ComprehensionBlock: 'ComprehensionBlock',
        ComprehensionExpression: 'ComprehensionExpression',
        ConditionalExpression: 'ConditionalExpression',
        ContinueStatement: 'ContinueStatement',
        DebuggerStatement: 'DebuggerStatement',
        DoWhileStatement: 'DoWhileStatement',
        EmptyStatement: 'EmptyStatement',
        ExportDeclaration: 'ExportDeclaration',
        ExportBatchSpecifier: 'ExportBatchSpecifier',
        ExportSpecifier: 'ExportSpecifier',
        ExpressionStatement: 'ExpressionStatement',
        ForInStatement: 'ForInStatement',
        ForOfStatement: 'ForOfStatement',
        ForStatement: 'ForStatement',
        FunctionDeclaration: 'FunctionDeclaration',
        FunctionExpression: 'FunctionExpression',
        Identifier: 'Identifier',
        IfStatement: 'IfStatement',
        ImportDeclaration: 'ImportDeclaration',
        ImportDefaultSpecifier: 'ImportDefaultSpecifier',
        ImportNamespaceSpecifier: 'ImportNamespaceSpecifier',
        ImportSpecifier: 'ImportSpecifier',
        LabeledStatement: 'LabeledStatement',
        Literal: 'Literal',
        LogicalExpression: 'LogicalExpression',
        MemberExpression: 'MemberExpression',
        MethodDefinition: 'MethodDefinition',
        ModuleSpecifier: 'ModuleSpecifier',
        NewExpression: 'NewExpression',
        ObjectExpression: 'ObjectExpression',
        ObjectPattern: 'ObjectPattern',
        ObjectTypeAnnotation: 'ObjectTypeAnnotation',
        OptionalParameter: 'OptionalParameter',
        ParametricTypeAnnotation: 'ParametricTypeAnnotation',
        ParametricallyTypedIdentifier: 'ParametricallyTypedIdentifier',
        Program: 'Program',
        Property: 'Property',
        ReturnStatement: 'ReturnStatement',
        SequenceExpression: 'SequenceExpression',
        SpreadElement: 'SpreadElement',
        SpreadProperty: 'SpreadProperty',
        SwitchCase: 'SwitchCase',
        SwitchStatement: 'SwitchStatement',
        TaggedTemplateExpression: 'TaggedTemplateExpression',
        TemplateElement: 'TemplateElement',
        TemplateLiteral: 'TemplateLiteral',
        ThisExpression: 'ThisExpression',
        ThrowStatement: 'ThrowStatement',
        TryStatement: 'TryStatement',
        TypeAnnotatedIdentifier: 'TypeAnnotatedIdentifier',
        TypeAnnotation: 'TypeAnnotation',
        UnaryExpression: 'UnaryExpression',
        UpdateExpression: 'UpdateExpression',
        VariableDeclaration: 'VariableDeclaration',
        VariableDeclarator: 'VariableDeclarator',
        VoidTypeAnnotation: 'VoidTypeAnnotation',
        WhileStatement: 'WhileStatement',
        WithStatement: 'WithStatement',
        XJSIdentifier: 'XJSIdentifier',
        XJSNamespacedName: 'XJSNamespacedName',
        XJSMemberExpression: 'XJSMemberExpression',
        XJSEmptyExpression: 'XJSEmptyExpression',
        XJSExpressionContainer: 'XJSExpressionContainer',
        XJSElement: 'XJSElement',
        XJSClosingElement: 'XJSClosingElement',
        XJSOpeningElement: 'XJSOpeningElement',
        XJSAttribute: 'XJSAttribute',
        XJSSpreadAttribute: 'XJSSpreadAttribute',
        XJSText: 'XJSText',
        YieldExpression: 'YieldExpression',
        AwaitExpression: 'AwaitExpression'
    };

    PropertyKind = {
        Data: 1,
        Get: 2,
        Set: 4
    };

    ClassPropertyType = {
        'static': 'static',
        prototype: 'prototype'
    };

    // Error messages should be identical to V8.
    Messages = {
        UnexpectedToken:  'Unexpected token %0',
        UnexpectedNumber:  'Unexpected number',
        UnexpectedString:  'Unexpected string',
        UnexpectedIdentifier:  'Unexpected identifier',
        UnexpectedReserved:  'Unexpected reserved word',
        UnexpectedTemplate:  'Unexpected quasi %0',
        UnexpectedEOS:  'Unexpected end of input',
        NewlineAfterThrow:  'Illegal newline after throw',
        InvalidRegExp: 'Invalid regular expression',
        UnterminatedRegExp:  'Invalid regular expression: missing /',
        InvalidLHSInAssignment:  'Invalid left-hand side in assignment',
        InvalidLHSInFormalsList:  'Invalid left-hand side in formals list',
        InvalidLHSInForIn:  'Invalid left-hand side in for-in',
        MultipleDefaultsInSwitch: 'More than one default clause in switch statement',
        NoCatchOrFinally:  'Missing catch or finally after try',
        UnknownLabel: 'Undefined label \'%0\'',
        Redeclaration: '%0 \'%1\' has already been declared',
        IllegalContinue: 'Illegal continue statement',
        IllegalBreak: 'Illegal break statement',
        IllegalDuplicateClassProperty: 'Illegal duplicate property in class definition',
        IllegalReturn: 'Illegal return statement',
        IllegalSpread: 'Illegal spread element',
        StrictModeWith:  'Strict mode code may not include a with statement',
        StrictCatchVariable:  'Catch variable may not be eval or arguments in strict mode',
        StrictVarName:  'Variable name may not be eval or arguments in strict mode',
        StrictParamName:  'Parameter name eval or arguments is not allowed in strict mode',
        StrictParamDupe: 'Strict mode function may not have duplicate parameter names',
        ParameterAfterRestParameter: 'Rest parameter must be final parameter of an argument list',
        DefaultRestParameter: 'Rest parameter can not have a default value',
        ElementAfterSpreadElement: 'Spread must be the final element of an element list',
        PropertyAfterSpreadProperty: 'A rest property must be the final property of an object literal',
        ObjectPatternAsRestParameter: 'Invalid rest parameter',
        ObjectPatternAsSpread: 'Invalid spread argument',
        StrictFunctionName:  'Function name may not be eval or arguments in strict mode',
        StrictOctalLiteral:  'Octal literals are not allowed in strict mode.',
        StrictDelete:  'Delete of an unqualified identifier in strict mode.',
        StrictDuplicateProperty:  'Duplicate data property in object literal not allowed in strict mode',
        AccessorDataProperty:  'Object literal may not have data and accessor property with the same name',
        AccessorGetSet:  'Object literal may not have multiple get/set accessors with the same name',
        StrictLHSAssignment:  'Assignment to eval or arguments is not allowed in strict mode',
        StrictLHSPostfix:  'Postfix increment/decrement may not have eval or arguments operand in strict mode',
        StrictLHSPrefix:  'Prefix increment/decrement may not have eval or arguments operand in strict mode',
        StrictReservedWord:  'Use of future reserved word in strict mode',
        MissingFromClause: 'Missing from clause',
        NoAsAfterImportNamespace: 'Missing as after import *',
        InvalidModuleSpecifier: 'Invalid module specifier',
        NoUnintializedConst: 'Const must be initialized',
        ComprehensionRequiresBlock: 'Comprehension must have at least one block',
        ComprehensionError:  'Comprehension Error',
        EachNotAllowed:  'Each is not supported',
        InvalidXJSAttributeValue: 'XJS value should be either an expression or a quoted XJS text',
        ExpectedXJSClosingTag: 'Expected corresponding XJS closing tag for %0',
        AdjacentXJSElements: 'Adjacent XJS elements must be wrapped in an enclosing tag'
    };

    // See also tools/generate-unicode-regex.py.
    Regex = {
        NonAsciiIdentifierStart: new RegExp('[\xaa\xb5\xba\xc0-\xd6\xd8-\xf6\xf8-\u02c1\u02c6-\u02d1\u02e0-\u02e4\u02ec\u02ee\u0370-\u0374\u0376\u0377\u037a-\u037d\u0386\u0388-\u038a\u038c\u038e-\u03a1\u03a3-\u03f5\u03f7-\u0481\u048a-\u0527\u0531-\u0556\u0559\u0561-\u0587\u05d0-\u05ea\u05f0-\u05f2\u0620-\u064a\u066e\u066f\u0671-\u06d3\u06d5\u06e5\u06e6\u06ee\u06ef\u06fa-\u06fc\u06ff\u0710\u0712-\u072f\u074d-\u07a5\u07b1\u07ca-\u07ea\u07f4\u07f5\u07fa\u0800-\u0815\u081a\u0824\u0828\u0840-\u0858\u08a0\u08a2-\u08ac\u0904-\u0939\u093d\u0950\u0958-\u0961\u0971-\u0977\u0979-\u097f\u0985-\u098c\u098f\u0990\u0993-\u09a8\u09aa-\u09b0\u09b2\u09b6-\u09b9\u09bd\u09ce\u09dc\u09dd\u09df-\u09e1\u09f0\u09f1\u0a05-\u0a0a\u0a0f\u0a10\u0a13-\u0a28\u0a2a-\u0a30\u0a32\u0a33\u0a35\u0a36\u0a38\u0a39\u0a59-\u0a5c\u0a5e\u0a72-\u0a74\u0a85-\u0a8d\u0a8f-\u0a91\u0a93-\u0aa8\u0aaa-\u0ab0\u0ab2\u0ab3\u0ab5-\u0ab9\u0abd\u0ad0\u0ae0\u0ae1\u0b05-\u0b0c\u0b0f\u0b10\u0b13-\u0b28\u0b2a-\u0b30\u0b32\u0b33\u0b35-\u0b39\u0b3d\u0b5c\u0b5d\u0b5f-\u0b61\u0b71\u0b83\u0b85-\u0b8a\u0b8e-\u0b90\u0b92-\u0b95\u0b99\u0b9a\u0b9c\u0b9e\u0b9f\u0ba3\u0ba4\u0ba8-\u0baa\u0bae-\u0bb9\u0bd0\u0c05-\u0c0c\u0c0e-\u0c10\u0c12-\u0c28\u0c2a-\u0c33\u0c35-\u0c39\u0c3d\u0c58\u0c59\u0c60\u0c61\u0c85-\u0c8c\u0c8e-\u0c90\u0c92-\u0ca8\u0caa-\u0cb3\u0cb5-\u0cb9\u0cbd\u0cde\u0ce0\u0ce1\u0cf1\u0cf2\u0d05-\u0d0c\u0d0e-\u0d10\u0d12-\u0d3a\u0d3d\u0d4e\u0d60\u0d61\u0d7a-\u0d7f\u0d85-\u0d96\u0d9a-\u0db1\u0db3-\u0dbb\u0dbd\u0dc0-\u0dc6\u0e01-\u0e30\u0e32\u0e33\u0e40-\u0e46\u0e81\u0e82\u0e84\u0e87\u0e88\u0e8a\u0e8d\u0e94-\u0e97\u0e99-\u0e9f\u0ea1-\u0ea3\u0ea5\u0ea7\u0eaa\u0eab\u0ead-\u0eb0\u0eb2\u0eb3\u0ebd\u0ec0-\u0ec4\u0ec6\u0edc-\u0edf\u0f00\u0f40-\u0f47\u0f49-\u0f6c\u0f88-\u0f8c\u1000-\u102a\u103f\u1050-\u1055\u105a-\u105d\u1061\u1065\u1066\u106e-\u1070\u1075-\u1081\u108e\u10a0-\u10c5\u10c7\u10cd\u10d0-\u10fa\u10fc-\u1248\u124a-\u124d\u1250-\u1256\u1258\u125a-\u125d\u1260-\u1288\u128a-\u128d\u1290-\u12b0\u12b2-\u12b5\u12b8-\u12be\u12c0\u12c2-\u12c5\u12c8-\u12d6\u12d8-\u1310\u1312-\u1315\u1318-\u135a\u1380-\u138f\u13a0-\u13f4\u1401-\u166c\u166f-\u167f\u1681-\u169a\u16a0-\u16ea\u16ee-\u16f0\u1700-\u170c\u170e-\u1711\u1720-\u1731\u1740-\u1751\u1760-\u176c\u176e-\u1770\u1780-\u17b3\u17d7\u17dc\u1820-\u1877\u1880-\u18a8\u18aa\u18b0-\u18f5\u1900-\u191c\u1950-\u196d\u1970-\u1974\u1980-\u19ab\u19c1-\u19c7\u1a00-\u1a16\u1a20-\u1a54\u1aa7\u1b05-\u1b33\u1b45-\u1b4b\u1b83-\u1ba0\u1bae\u1baf\u1bba-\u1be5\u1c00-\u1c23\u1c4d-\u1c4f\u1c5a-\u1c7d\u1ce9-\u1cec\u1cee-\u1cf1\u1cf5\u1cf6\u1d00-\u1dbf\u1e00-\u1f15\u1f18-\u1f1d\u1f20-\u1f45\u1f48-\u1f4d\u1f50-\u1f57\u1f59\u1f5b\u1f5d\u1f5f-\u1f7d\u1f80-\u1fb4\u1fb6-\u1fbc\u1fbe\u1fc2-\u1fc4\u1fc6-\u1fcc\u1fd0-\u1fd3\u1fd6-\u1fdb\u1fe0-\u1fec\u1ff2-\u1ff4\u1ff6-\u1ffc\u2071\u207f\u2090-\u209c\u2102\u2107\u210a-\u2113\u2115\u2119-\u211d\u2124\u2126\u2128\u212a-\u212d\u212f-\u2139\u213c-\u213f\u2145-\u2149\u214e\u2160-\u2188\u2c00-\u2c2e\u2c30-\u2c5e\u2c60-\u2ce4\u2ceb-\u2cee\u2cf2\u2cf3\u2d00-\u2d25\u2d27\u2d2d\u2d30-\u2d67\u2d6f\u2d80-\u2d96\u2da0-\u2da6\u2da8-\u2dae\u2db0-\u2db6\u2db8-\u2dbe\u2dc0-\u2dc6\u2dc8-\u2dce\u2dd0-\u2dd6\u2dd8-\u2dde\u2e2f\u3005-\u3007\u3021-\u3029\u3031-\u3035\u3038-\u303c\u3041-\u3096\u309d-\u309f\u30a1-\u30fa\u30fc-\u30ff\u3105-\u312d\u3131-\u318e\u31a0-\u31ba\u31f0-\u31ff\u3400-\u4db5\u4e00-\u9fcc\ua000-\ua48c\ua4d0-\ua4fd\ua500-\ua60c\ua610-\ua61f\ua62a\ua62b\ua640-\ua66e\ua67f-\ua697\ua6a0-\ua6ef\ua717-\ua71f\ua722-\ua788\ua78b-\ua78e\ua790-\ua793\ua7a0-\ua7aa\ua7f8-\ua801\ua803-\ua805\ua807-\ua80a\ua80c-\ua822\ua840-\ua873\ua882-\ua8b3\ua8f2-\ua8f7\ua8fb\ua90a-\ua925\ua930-\ua946\ua960-\ua97c\ua984-\ua9b2\ua9cf\uaa00-\uaa28\uaa40-\uaa42\uaa44-\uaa4b\uaa60-\uaa76\uaa7a\uaa80-\uaaaf\uaab1\uaab5\uaab6\uaab9-\uaabd\uaac0\uaac2\uaadb-\uaadd\uaae0-\uaaea\uaaf2-\uaaf4\uab01-\uab06\uab09-\uab0e\uab11-\uab16\uab20-\uab26\uab28-\uab2e\uabc0-\uabe2\uac00-\ud7a3\ud7b0-\ud7c6\ud7cb-\ud7fb\uf900-\ufa6d\ufa70-\ufad9\ufb00-\ufb06\ufb13-\ufb17\ufb1d\ufb1f-\ufb28\ufb2a-\ufb36\ufb38-\ufb3c\ufb3e\ufb40\ufb41\ufb43\ufb44\ufb46-\ufbb1\ufbd3-\ufd3d\ufd50-\ufd8f\ufd92-\ufdc7\ufdf0-\ufdfb\ufe70-\ufe74\ufe76-\ufefc\uff21-\uff3a\uff41-\uff5a\uff66-\uffbe\uffc2-\uffc7\uffca-\uffcf\uffd2-\uffd7\uffda-\uffdc]'),
        NonAsciiIdentifierPart: new 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\uffc7\uffca-\uffcf\uffd2-\uffd7\uffda-\uffdc]'),
        LeadingZeros: new RegExp('^0+(?!$)')
    };

    // Ensure the condition is true, otherwise throw an error.
    // This is only to have a better contract semantic, i.e. another safety net
    // to catch a logic error. The condition shall be fulfilled in normal case.
    // Do NOT use this to enforce a certain condition on any user input.

    function assert(condition, message) {
        if (!condition) {
            throw new Error('ASSERT: ' + message);
        }
    }

    function isDecimalDigit(ch) {
        return (ch >= 48 && ch <= 57);   // 0..9
    }

    function isHexDigit(ch) {
        return '0123456789abcdefABCDEF'.indexOf(ch) >= 0;
    }

    function isOctalDigit(ch) {
        return '01234567'.indexOf(ch) >= 0;
    }


    // 7.2 White Space

    function isWhiteSpace(ch) {
        return (ch === 32) ||  // space
            (ch === 9) ||      // tab
            (ch === 0xB) ||
            (ch === 0xC) ||
            (ch === 0xA0) ||
            (ch >= 0x1680 && '\u1680\u180E\u2000\u2001\u2002\u2003\u2004\u2005\u2006\u2007\u2008\u2009\u200A\u202F\u205F\u3000\uFEFF'.indexOf(String.fromCharCode(ch)) > 0);
    }

    // 7.3 Line Terminators

    function isLineTerminator(ch) {
        return (ch === 10) || (ch === 13) || (ch === 0x2028) || (ch === 0x2029);
    }

    // 7.6 Identifier Names and Identifiers

    function isIdentifierStart(ch) {
        return (ch === 36) || (ch === 95) ||  // $ (dollar) and _ (underscore)
            (ch >= 65 && ch <= 90) ||         // A..Z
            (ch >= 97 && ch <= 122) ||        // a..z
            (ch === 92) ||                    // \ (backslash)
            ((ch >= 0x80) && Regex.NonAsciiIdentifierStart.test(String.fromCharCode(ch)));
    }

    function isIdentifierPart(ch) {
        return (ch === 36) || (ch === 95) ||  // $ (dollar) and _ (underscore)
            (ch >= 65 && ch <= 90) ||         // A..Z
            (ch >= 97 && ch <= 122) ||        // a..z
            (ch >= 48 && ch <= 57) ||         // 0..9
            (ch === 92) ||                    // \ (backslash)
            ((ch >= 0x80) && Regex.NonAsciiIdentifierPart.test(String.fromCharCode(ch)));
    }

    // 7.6.1.2 Future Reserved Words

    function isFutureReservedWord(id) {
        switch (id) {
        case 'class':
        case 'enum':
        case 'export':
        case 'extends':
        case 'import':
        case 'super':
            return true;
        default:
            return false;
        }
    }

    function isStrictModeReservedWord(id) {
        switch (id) {
        case 'implements':
        case 'interface':
        case 'package':
        case 'private':
        case 'protected':
        case 'public':
        case 'static':
        case 'yield':
        case 'let':
            return true;
        default:
            return false;
        }
    }

    function isRestrictedWord(id) {
        return id === 'eval' || id === 'arguments';
    }

    // 7.6.1.1 Keywords

    function isKeyword(id) {
        if (strict && isStrictModeReservedWord(id)) {
            return true;
        }

        // 'const' is specialized as Keyword in V8.
        // 'yield' is only treated as a keyword in strict mode.
        // 'let' is for compatiblity with SpiderMonkey and ES.next.
        // Some others are from future reserved words.

        switch (id.length) {
        case 2:
            return (id === 'if') || (id === 'in') || (id === 'do');
        case 3:
            return (id === 'var') || (id === 'for') || (id === 'new') ||
                (id === 'try') || (id === 'let');
        case 4:
            return (id === 'this') || (id === 'else') || (id === 'case') ||
                (id === 'void') || (id === 'with') || (id === 'enum');
        case 5:
            return (id === 'while') || (id === 'break') || (id === 'catch') ||
                (id === 'throw') || (id === 'const') ||
                (id === 'class') || (id === 'super');
        case 6:
            return (id === 'return') || (id === 'typeof') || (id === 'delete') ||
                (id === 'switch') || (id === 'export') || (id === 'import');
        case 7:
            return (id === 'default') || (id === 'finally') || (id === 'extends');
        case 8:
            return (id === 'function') || (id === 'continue') || (id === 'debugger');
        case 10:
            return (id === 'instanceof');
        default:
            return false;
        }
    }

    // 7.4 Comments

    function skipComment() {
        var ch, blockComment, lineComment;

        blockComment = false;
        lineComment = false;

        while (index < length) {
            ch = source.charCodeAt(index);

            if (lineComment) {
                ++index;
                if (isLineTerminator(ch)) {
                    lineComment = false;
                    if (ch === 13 && source.charCodeAt(index) === 10) {
                        ++index;
                    }
                    ++lineNumber;
                    lineStart = index;
                }
            } else if (blockComment) {
                if (isLineTerminator(ch)) {
                    if (ch === 13) {
                        ++index;
                    }
                    if (ch !== 13 || source.charCodeAt(index) === 10) {
                        ++lineNumber;
                        ++index;
                        lineStart = index;
                        if (index >= length) {
                            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
                        }
                    }
                } else {
                    ch = source.charCodeAt(index++);
                    if (index >= length) {
                        throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
                    }
                    // Block comment ends with '*/' (char #42, char #47).
                    if (ch === 42) {
                        ch = source.charCodeAt(index);
                        if (ch === 47) {
                            ++index;
                            blockComment = false;
                        }
                    }
                }
            } else if (ch === 47) {
                ch = source.charCodeAt(index + 1);
                // Line comment starts with '//' (char #47, char #47).
                if (ch === 47) {
                    index += 2;
                    lineComment = true;
                } else if (ch === 42) {
                    // Block comment starts with '/*' (char #47, char #42).
                    index += 2;
                    blockComment = true;
                    if (index >= length) {
                        throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
                    }
                } else {
                    break;
                }
            } else if (isWhiteSpace(ch)) {
                ++index;
            } else if (isLineTerminator(ch)) {
                ++index;
                if (ch === 13 && source.charCodeAt(index) === 10) {
                    ++index;
                }
                ++lineNumber;
                lineStart = index;
            } else {
                break;
            }
        }
    }

    function scanHexEscape(prefix) {
        var i, len, ch, code = 0;

        len = (prefix === 'u') ? 4 : 2;
        for (i = 0; i < len; ++i) {
            if (index < length && isHexDigit(source[index])) {
                ch = source[index++];
                code = code * 16 + '0123456789abcdef'.indexOf(ch.toLowerCase());
            } else {
                return '';
            }
        }
        return String.fromCharCode(code);
    }

    function scanUnicodeCodePointEscape() {
        var ch, code, cu1, cu2;

        ch = source[index];
        code = 0;

        // At least, one hex digit is required.
        if (ch === '}') {
            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
        }

        while (index < length) {
            ch = source[index++];
            if (!isHexDigit(ch)) {
                break;
            }
            code = code * 16 + '0123456789abcdef'.indexOf(ch.toLowerCase());
        }

        if (code > 0x10FFFF || ch !== '}') {
            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
        }

        // UTF-16 Encoding
        if (code <= 0xFFFF) {
            return String.fromCharCode(code);
        }
        cu1 = ((code - 0x10000) >> 10) + 0xD800;
        cu2 = ((code - 0x10000) & 1023) + 0xDC00;
        return String.fromCharCode(cu1, cu2);
    }

    function getEscapedIdentifier() {
        var ch, id;

        ch = source.charCodeAt(index++);
        id = String.fromCharCode(ch);

        // '\u' (char #92, char #117) denotes an escaped character.
        if (ch === 92) {
            if (source.charCodeAt(index) !== 117) {
                throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
            }
            ++index;
            ch = scanHexEscape('u');
            if (!ch || ch === '\\' || !isIdentifierStart(ch.charCodeAt(0))) {
                throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
            }
            id = ch;
        }

        while (index < length) {
            ch = source.charCodeAt(index);
            if (!isIdentifierPart(ch)) {
                break;
            }
            ++index;
            id += String.fromCharCode(ch);

            // '\u' (char #92, char #117) denotes an escaped character.
            if (ch === 92) {
                id = id.substr(0, id.length - 1);
                if (source.charCodeAt(index) !== 117) {
                    throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
                }
                ++index;
                ch = scanHexEscape('u');
                if (!ch || ch === '\\' || !isIdentifierPart(ch.charCodeAt(0))) {
                    throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
                }
                id += ch;
            }
        }

        return id;
    }

    function getIdentifier() {
        var start, ch;

        start = index++;
        while (index < length) {
            ch = source.charCodeAt(index);
            if (ch === 92) {
                // Blackslash (char #92) marks Unicode escape sequence.
                index = start;
                return getEscapedIdentifier();
            }
            if (isIdentifierPart(ch)) {
                ++index;
            } else {
                break;
            }
        }

        return source.slice(start, index);
    }

    function scanIdentifier() {
        var start, id, type;

        start = index;

        // Backslash (char #92) starts an escaped character.
        id = (source.charCodeAt(index) === 92) ? getEscapedIdentifier() : getIdentifier();

        // There is no keyword or literal with only one character.
        // Thus, it must be an identifier.
        if (id.length === 1) {
            type = Token.Identifier;
        } else if (isKeyword(id)) {
            type = Token.Keyword;
        } else if (id === 'null') {
            type = Token.NullLiteral;
        } else if (id === 'true' || id === 'false') {
            type = Token.BooleanLiteral;
        } else {
            type = Token.Identifier;
        }

        return {
            type: type,
            value: id,
            lineNumber: lineNumber,
            lineStart: lineStart,
            range: [start, index]
        };
    }


    // 7.7 Punctuators

    function scanPunctuator() {
        var start = index,
            code = source.charCodeAt(index),
            code2,
            ch1 = source[index],
            ch2,
            ch3,
            ch4;

        switch (code) {
        // Check for most common single-character punctuators.
        case 40:   // ( open bracket
        case 41:   // ) close bracket
        case 59:   // ; semicolon
        case 44:   // , comma
        case 123:  // { open curly brace
        case 125:  // } close curly brace
        case 91:   // [
        case 93:   // ]
        case 58:   // :
        case 63:   // ?
        case 126:  // ~
            ++index;
            if (extra.tokenize) {
                if (code === 40) {
                    extra.openParenToken = extra.tokens.length;
                } else if (code === 123) {
                    extra.openCurlyToken = extra.tokens.length;
                }
            }
            return {
                type: Token.Punctuator,
                value: String.fromCharCode(code),
                lineNumber: lineNumber,
                lineStart: lineStart,
                range: [start, index]
            };

        default:
            code2 = source.charCodeAt(index + 1);

            // '=' (char #61) marks an assignment or comparison operator.
            if (code2 === 61) {
                switch (code) {
                case 37:  // %
                case 38:  // &
                case 42:  // *:
                case 43:  // +
                case 45:  // -
                case 47:  // /
                case 60:  // <
                case 62:  // >
                case 94:  // ^
                case 124: // |
                    index += 2;
                    return {
                        type: Token.Punctuator,
                        value: String.fromCharCode(code) + String.fromCharCode(code2),
                        lineNumber: lineNumber,
                        lineStart: lineStart,
                        range: [start, index]
                    };

                case 33: // !
                case 61: // =
                    index += 2;

                    // !== and ===
                    if (source.charCodeAt(index) === 61) {
                        ++index;
                    }
                    return {
                        type: Token.Punctuator,
                        value: source.slice(start, index),
                        lineNumber: lineNumber,
                        lineStart: lineStart,
                        range: [start, index]
                    };
                default:
                    break;
                }
            }
            break;
        }

        // Peek more characters.

        ch2 = source[index + 1];
        ch3 = source[index + 2];
        ch4 = source[index + 3];

        // 4-character punctuator: >>>=

        if (ch1 === '>' && ch2 === '>' && ch3 === '>') {
            if (ch4 === '=') {
                index += 4;
                return {
                    type: Token.Punctuator,
                    value: '>>>=',
                    lineNumber: lineNumber,
                    lineStart: lineStart,
                    range: [start, index]
                };
            }
        }

        // 3-character punctuators: === !== >>> <<= >>=

        if (ch1 === '>' && ch2 === '>' && ch3 === '>') {
            index += 3;
            return {
                type: Token.Punctuator,
                value: '>>>',
                lineNumber: lineNumber,
                lineStart: lineStart,
                range: [start, index]
            };
        }

        if (ch1 === '<' && ch2 === '<' && ch3 === '=') {
            index += 3;
            return {
                type: Token.Punctuator,
                value: '<<=',
                lineNumber: lineNumber,
                lineStart: lineStart,
                range: [start, index]
            };
        }

        if (ch1 === '>' && ch2 === '>' && ch3 === '=') {
            index += 3;
            return {
                type: Token.Punctuator,
                value: '>>=',
                lineNumber: lineNumber,
                lineStart: lineStart,
                range: [start, index]
            };
        }

        if (ch1 === '.' && ch2 === '.' && ch3 === '.') {
            index += 3;
            return {
                type: Token.Punctuator,
                value: '...',
                lineNumber: lineNumber,
                lineStart: lineStart,
                range: [start, index]
            };
        }

        // Other 2-character punctuators: ++ -- << >> && ||

        if (ch1 === ch2 && ('+-<>&|'.indexOf(ch1) >= 0)) {
            index += 2;
            return {
                type: Token.Punctuator,
                value: ch1 + ch2,
                lineNumber: lineNumber,
                lineStart: lineStart,
                range: [start, index]
            };
        }

        if (ch1 === '=' && ch2 === '>') {
            index += 2;
            return {
                type: Token.Punctuator,
                value: '=>',
                lineNumber: lineNumber,
                lineStart: lineStart,
                range: [start, index]
            };
        }

        if ('<>=!+-*%&|^/'.indexOf(ch1) >= 0) {
            ++index;
            return {
                type: Token.Punctuator,
                value: ch1,
                lineNumber: lineNumber,
                lineStart: lineStart,
                range: [start, index]
            };
        }

        if (ch1 === '.') {
            ++index;
            return {
                type: Token.Punctuator,
                value: ch1,
                lineNumber: lineNumber,
                lineStart: lineStart,
                range: [start, index]
            };
        }

        throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
    }

    // 7.8.3 Numeric Literals

    function scanHexLiteral(start) {
        var number = '';

        while (index < length) {
            if (!isHexDigit(source[index])) {
                break;
            }
            number += source[index++];
        }

        if (number.length === 0) {
            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
        }

        if (isIdentifierStart(source.charCodeAt(index))) {
            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
        }

        return {
            type: Token.NumericLiteral,
            value: parseInt('0x' + number, 16),
            lineNumber: lineNumber,
            lineStart: lineStart,
            range: [start, index]
        };
    }

    function scanOctalLiteral(prefix, start) {
        var number, octal;

        if (isOctalDigit(prefix)) {
            octal = true;
            number = '0' + source[index++];
        } else {
            octal = false;
            ++index;
            number = '';
        }

        while (index < length) {
            if (!isOctalDigit(source[index])) {
                break;
            }
            number += source[index++];
        }

        if (!octal && number.length === 0) {
            // only 0o or 0O
            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
        }

        if (isIdentifierStart(source.charCodeAt(index)) || isDecimalDigit(source.charCodeAt(index))) {
            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
        }

        return {
            type: Token.NumericLiteral,
            value: parseInt(number, 8),
            octal: octal,
            lineNumber: lineNumber,
            lineStart: lineStart,
            range: [start, index]
        };
    }

    function scanNumericLiteral() {
        var number, start, ch, octal;

        ch = source[index];
        assert(isDecimalDigit(ch.charCodeAt(0)) || (ch === '.'),
            'Numeric literal must start with a decimal digit or a decimal point');

        start = index;
        number = '';
        if (ch !== '.') {
            number = source[index++];
            ch = source[index];

            // Hex number starts with '0x'.
            // Octal number starts with '0'.
            // Octal number in ES6 starts with '0o'.
            // Binary number in ES6 starts with '0b'.
            if (number === '0') {
                if (ch === 'x' || ch === 'X') {
                    ++index;
                    return scanHexLiteral(start);
                }
                if (ch === 'b' || ch === 'B') {
                    ++index;
                    number = '';

                    while (index < length) {
                        ch = source[index];
                        if (ch !== '0' && ch !== '1') {
                            break;
                        }
                        number += source[index++];
                    }

                    if (number.length === 0) {
                        // only 0b or 0B
                        throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
                    }

                    if (index < length) {
                        ch = source.charCodeAt(index);
                        if (isIdentifierStart(ch) || isDecimalDigit(ch)) {
                            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
                        }
                    }
                    return {
                        type: Token.NumericLiteral,
                        value: parseInt(number, 2),
                        lineNumber: lineNumber,
                        lineStart: lineStart,
                        range: [start, index]
                    };
                }
                if (ch === 'o' || ch === 'O' || isOctalDigit(ch)) {
                    return scanOctalLiteral(ch, start);
                }
                // decimal number starts with '0' such as '09' is illegal.
                if (ch && isDecimalDigit(ch.charCodeAt(0))) {
                    throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
                }
            }

            while (isDecimalDigit(source.charCodeAt(index))) {
                number += source[index++];
            }
            ch = source[index];
        }

        if (ch === '.') {
            number += source[index++];
            while (isDecimalDigit(source.charCodeAt(index))) {
                number += source[index++];
            }
            ch = source[index];
        }

        if (ch === 'e' || ch === 'E') {
            number += source[index++];

            ch = source[index];
            if (ch === '+' || ch === '-') {
                number += source[index++];
            }
            if (isDecimalDigit(source.charCodeAt(index))) {
                while (isDecimalDigit(source.charCodeAt(index))) {
                    number += source[index++];
                }
            } else {
                throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
            }
        }

        if (isIdentifierStart(source.charCodeAt(index))) {
            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
        }

        return {
            type: Token.NumericLiteral,
            value: parseFloat(number),
            lineNumber: lineNumber,
            lineStart: lineStart,
            range: [start, index]
        };
    }

    // 7.8.4 String Literals

    function scanStringLiteral() {
        var str = '', quote, start, ch, code, unescaped, restore, octal = false;

        quote = source[index];
        assert((quote === '\'' || quote === '"'),
            'String literal must starts with a quote');

        start = index;
        ++index;

        while (index < length) {
            ch = source[index++];

            if (ch === quote) {
                quote = '';
                break;
            } else if (ch === '\\') {
                ch = source[index++];
                if (!ch || !isLineTerminator(ch.charCodeAt(0))) {
                    switch (ch) {
                    case 'n':
                        str += '\n';
                        break;
                    case 'r':
                        str += '\r';
                        break;
                    case 't':
                        str += '\t';
                        break;
                    case 'u':
                    case 'x':
                        if (source[index] === '{') {
                            ++index;
                            str += scanUnicodeCodePointEscape();
                        } else {
                            restore = index;
                            unescaped = scanHexEscape(ch);
                            if (unescaped) {
                                str += unescaped;
                            } else {
                                index = restore;
                                str += ch;
                            }
                        }
                        break;
                    case 'b':
                        str += '\b';
                        break;
                    case 'f':
                        str += '\f';
                        break;
                    case 'v':
                        str += '\x0B';
                        break;

                    default:
                        if (isOctalDigit(ch)) {
                            code = '01234567'.indexOf(ch);

                            // \0 is not octal escape sequence
                            if (code !== 0) {
                                octal = true;
                            }

                            if (index < length && isOctalDigit(source[index])) {
                                octal = true;
                                code = code * 8 + '01234567'.indexOf(source[index++]);

                                // 3 digits are only allowed when string starts
                                // with 0, 1, 2, 3
                                if ('0123'.indexOf(ch) >= 0 &&
                                        index < length &&
                                        isOctalDigit(source[index])) {
                                    code = code * 8 + '01234567'.indexOf(source[index++]);
                                }
                            }
                            str += String.fromCharCode(code);
                        } else {
                            str += ch;
                        }
                        break;
                    }
                } else {
                    ++lineNumber;
                    if (ch ===  '\r' && source[index] === '\n') {
                        ++index;
                    }
                    lineStart = index;
                }
            } else if (isLineTerminator(ch.charCodeAt(0))) {
                break;
            } else {
                str += ch;
            }
        }

        if (quote !== '') {
            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
        }

        return {
            type: Token.StringLiteral,
            value: str,
            octal: octal,
            lineNumber: lineNumber,
            lineStart: lineStart,
            range: [start, index]
        };
    }

    function scanTemplate() {
        var cooked = '', ch, start, terminated, tail, restore, unescaped, code, octal;

        terminated = false;
        tail = false;
        start = index;

        ++index;

        while (index < length) {
            ch = source[index++];
            if (ch === '`') {
                tail = true;
                terminated = true;
                break;
            } else if (ch === '$') {
                if (source[index] === '{') {
                    ++index;
                    terminated = true;
                    break;
                }
                cooked += ch;
            } else if (ch === '\\') {
                ch = source[index++];
                if (!isLineTerminator(ch.charCodeAt(0))) {
                    switch (ch) {
                    case 'n':
                        cooked += '\n';
                        break;
                    case 'r':
                        cooked += '\r';
                        break;
                    case 't':
                        cooked += '\t';
                        break;
                    case 'u':
                    case 'x':
                        if (source[index] === '{') {
                            ++index;
                            cooked += scanUnicodeCodePointEscape();
                        } else {
                            restore = index;
                            unescaped = scanHexEscape(ch);
                            if (unescaped) {
                                cooked += unescaped;
                            } else {
                                index = restore;
                                cooked += ch;
                            }
                        }
                        break;
                    case 'b':
                        cooked += '\b';
                        break;
                    case 'f':
                        cooked += '\f';
                        break;
                    case 'v':
                        cooked += '\v';
                        break;

                    default:
                        if (isOctalDigit(ch)) {
                            code = '01234567'.indexOf(ch);

                            // \0 is not octal escape sequence
                            if (code !== 0) {
                                octal = true;
                            }

                            if (index < length && isOctalDigit(source[index])) {
                                octal = true;
                                code = code * 8 + '01234567'.indexOf(source[index++]);

                                // 3 digits are only allowed when string starts
                                // with 0, 1, 2, 3
                                if ('0123'.indexOf(ch) >= 0 &&
                                        index < length &&
                                        isOctalDigit(source[index])) {
                                    code = code * 8 + '01234567'.indexOf(source[index++]);
                                }
                            }
                            cooked += String.fromCharCode(code);
                        } else {
                            cooked += ch;
                        }
                        break;
                    }
                } else {
                    ++lineNumber;
                    if (ch ===  '\r' && source[index] === '\n') {
                        ++index;
                    }
                    lineStart = index;
                }
            } else if (isLineTerminator(ch.charCodeAt(0))) {
                ++lineNumber;
                if (ch ===  '\r' && source[index] === '\n') {
                    ++index;
                }
                lineStart = index;
                cooked += '\n';
            } else {
                cooked += ch;
            }
        }

        if (!terminated) {
            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
        }

        return {
            type: Token.Template,
            value: {
                cooked: cooked,
                raw: source.slice(start + 1, index - ((tail) ? 1 : 2))
            },
            tail: tail,
            octal: octal,
            lineNumber: lineNumber,
            lineStart: lineStart,
            range: [start, index]
        };
    }

    function scanTemplateElement(option) {
        var startsWith, template;

        lookahead = null;
        skipComment();

        startsWith = (option.head) ? '`' : '}';

        if (source[index] !== startsWith) {
            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
        }

        template = scanTemplate();

        peek();

        return template;
    }

    function scanRegExp() {
        var str, ch, start, pattern, flags, value, classMarker = false, restore, terminated = false, tmp;

        lookahead = null;
        skipComment();

        start = index;
        ch = source[index];
        assert(ch === '/', 'Regular expression literal must start with a slash');
        str = source[index++];

        while (index < length) {
            ch = source[index++];
            str += ch;
            if (classMarker) {
                if (ch === ']') {
                    classMarker = false;
                }
            } else {
                if (ch === '\\') {
                    ch = source[index++];
                    // ECMA-262 7.8.5
                    if (isLineTerminator(ch.charCodeAt(0))) {
                        throwError({}, Messages.UnterminatedRegExp);
                    }
                    str += ch;
                } else if (ch === '/') {
                    terminated = true;
                    break;
                } else if (ch === '[') {
                    classMarker = true;
                } else if (isLineTerminator(ch.charCodeAt(0))) {
                    throwError({}, Messages.UnterminatedRegExp);
                }
            }
        }

        if (!terminated) {
            throwError({}, Messages.UnterminatedRegExp);
        }

        // Exclude leading and trailing slash.
        pattern = str.substr(1, str.length - 2);

        flags = '';
        while (index < length) {
            ch = source[index];
            if (!isIdentifierPart(ch.charCodeAt(0))) {
                break;
            }

            ++index;
            if (ch === '\\' && index < length) {
                ch = source[index];
                if (ch === 'u') {
                    ++index;
                    restore = index;
                    ch = scanHexEscape('u');
                    if (ch) {
                        flags += ch;
                        for (str += '\\u'; restore < index; ++restore) {
                            str += source[restore];
                        }
                    } else {
                        index = restore;
                        flags += 'u';
                        str += '\\u';
                    }
                } else {
                    str += '\\';
                }
            } else {
                flags += ch;
                str += ch;
            }
        }

        tmp = pattern;
        if (flags.indexOf('u') >= 0) {
            // Replace each astral symbol and every Unicode code point
            // escape sequence that represents such a symbol with a single
            // ASCII symbol to avoid throwing on regular expressions that
            // are only valid in combination with the `/u` flag.
            tmp = tmp
                .replace(/\\u\{([0-9a-fA-F]{5,6})\}/g, 'x')
                .replace(/[\uD800-\uDBFF][\uDC00-\uDFFF]/g, 'x');
        }

        // First, detect invalid regular expressions.
        try {
            value = new RegExp(tmp);
        } catch (e) {
            throwError({}, Messages.InvalidRegExp);
        }

        // Return a regular expression object for this pattern-flag pair, or
        // `null` in case the current environment doesn't support the flags it
        // uses.
        try {
            value = new RegExp(pattern, flags);
        } catch (exception) {
            value = null;
        }

        peek();

        if (extra.tokenize) {
            return {
                type: Token.RegularExpression,
                value: value,
                regex: {
                    pattern: pattern,
                    flags: flags
                },
                lineNumber: lineNumber,
                lineStart: lineStart,
                range: [start, index]
            };
        }
        return {
            literal: str,
            value: value,
            regex: {
                pattern: pattern,
                flags: flags
            },
            range: [start, index]
        };
    }

    function isIdentifierName(token) {
        return token.type === Token.Identifier ||
            token.type === Token.Keyword ||
            token.type === Token.BooleanLiteral ||
            token.type === Token.NullLiteral;
    }

    function advanceSlash() {
        var prevToken,
            checkToken;
        // Using the following algorithm:
        // https://github.com/mozilla/sweet.js/wiki/design
        prevToken = extra.tokens[extra.tokens.length - 1];
        if (!prevToken) {
            // Nothing before that: it cannot be a division.
            return scanRegExp();
        }
        if (prevToken.type === 'Punctuator') {
            if (prevToken.value === ')') {
                checkToken = extra.tokens[extra.openParenToken - 1];
                if (checkToken &&
                        checkToken.type === 'Keyword' &&
                        (checkToken.value === 'if' ||
                         checkToken.value === 'while' ||
                         checkToken.value === 'for' ||
                         checkToken.value === 'with')) {
                    return scanRegExp();
                }
                return scanPunctuator();
            }
            if (prevToken.value === '}') {
                // Dividing a function by anything makes little sense,
                // but we have to check for that.
                if (extra.tokens[extra.openCurlyToken - 3] &&
                        extra.tokens[extra.openCurlyToken - 3].type === 'Keyword') {
                    // Anonymous function.
                    checkToken = extra.tokens[extra.openCurlyToken - 4];
                    if (!checkToken) {
                        return scanPunctuator();
                    }
                } else if (extra.tokens[extra.openCurlyToken - 4] &&
                        extra.tokens[extra.openCurlyToken - 4].type === 'Keyword') {
                    // Named function.
                    checkToken = extra.tokens[extra.openCurlyToken - 5];
                    if (!checkToken) {
                        return scanRegExp();
                    }
                } else {
                    return scanPunctuator();
                }
                // checkToken determines whether the function is
                // a declaration or an expression.
                if (FnExprTokens.indexOf(checkToken.value) >= 0) {
                    // It is an expression.
                    return scanPunctuator();
                }
                // It is a declaration.
                return scanRegExp();
            }
            return scanRegExp();
        }
        if (prevToken.type === 'Keyword') {
            return scanRegExp();
        }
        return scanPunctuator();
    }

    function advance() {
        var ch;

        if (!state.inXJSChild) {
            skipComment();
        }

        if (index >= length) {
            return {
                type: Token.EOF,
                lineNumber: lineNumber,
                lineStart: lineStart,
                range: [index, index]
            };
        }

        if (state.inXJSChild) {
            return advanceXJSChild();
        }

        ch = source.charCodeAt(index);

        // Very common: ( and ) and ;
        if (ch === 40 || ch === 41 || ch === 58) {
            return scanPunctuator();
        }

        // String literal starts with single quote (#39) or double quote (#34).
        if (ch === 39 || ch === 34) {
            if (state.inXJSTag) {
                return scanXJSStringLiteral();
            }
            return scanStringLiteral();
        }

        if (state.inXJSTag && isXJSIdentifierStart(ch)) {
            return scanXJSIdentifier();
        }

        if (ch === 96) {
            return scanTemplate();
        }
        if (isIdentifierStart(ch)) {
            return scanIdentifier();
        }

        // Dot (.) char #46 can also start a floating-point number, hence the need
        // to check the next character.
        if (ch === 46) {
            if (isDecimalDigit(source.charCodeAt(index + 1))) {
                return scanNumericLiteral();
            }
            return scanPunctuator();
        }

        if (isDecimalDigit(ch)) {
            return scanNumericLiteral();
        }

        // Slash (/) char #47 can also start a regex.
        if (extra.tokenize && ch === 47) {
            return advanceSlash();
        }

        return scanPunctuator();
    }

    function lex() {
        var token;

        token = lookahead;
        index = token.range[1];
        lineNumber = token.lineNumber;
        lineStart = token.lineStart;

        lookahead = advance();

        index = token.range[1];
        lineNumber = token.lineNumber;
        lineStart = token.lineStart;

        return token;
    }

    function peek() {
        var pos, line, start;

        pos = index;
        line = lineNumber;
        start = lineStart;
        lookahead = advance();
        index = pos;
        lineNumber = line;
        lineStart = start;
    }

    function lookahead2() {
        var adv, pos, line, start, result;

        // If we are collecting the tokens, don't grab the next one yet.
        adv = (typeof extra.advance === 'function') ? extra.advance : advance;

        pos = index;
        line = lineNumber;
        start = lineStart;

        // Scan for the next immediate token.
        if (lookahead === null) {
            lookahead = adv();
        }
        index = lookahead.range[1];
        lineNumber = lookahead.lineNumber;
        lineStart = lookahead.lineStart;

        // Grab the token right after.
        result = adv();
        index = pos;
        lineNumber = line;
        lineStart = start;

        return result;
    }

    function rewind(token) {
        index = token.range[0];
        lineNumber = token.lineNumber;
        lineStart = token.lineStart;
        lookahead = token;
    }

    function markerCreate() {
        if (!extra.loc && !extra.range) {
            return undefined;
        }
        skipComment();
        return {offset: index, line: lineNumber, col: index - lineStart};
    }

    function markerCreatePreserveWhitespace() {
        if (!extra.loc && !extra.range) {
            return undefined;
        }
        return {offset: index, line: lineNumber, col: index - lineStart};
    }

    function processComment(node) {
        var lastChild,
            trailingComments,
            bottomRight = extra.bottomRightStack,
            last = bottomRight[bottomRight.length - 1];

        if (node.type === Syntax.Program) {
            if (node.body.length > 0) {
                return;
            }
        }

        if (extra.trailingComments.length > 0) {
            if (extra.trailingComments[0].range[0] >= node.range[1]) {
                trailingComments = extra.trailingComments;
                extra.trailingComments = [];
            } else {
                extra.trailingComments.length = 0;
            }
        } else {
            if (last && last.trailingComments && last.trailingComments[0].range[0] >= node.range[1]) {
                trailingComments = last.trailingComments;
                delete last.trailingComments;
            }
        }

        // Eating the stack.
        if (last) {
            while (last && last.range[0] >= node.range[0]) {
                lastChild = last;
                last = bottomRight.pop();
            }
        }

        if (lastChild) {
            if (lastChild.leadingComments && lastChild.leadingComments[lastChild.leadingComments.length - 1].range[1] <= node.range[0]) {
                node.leadingComments = lastChild.leadingComments;
                delete lastChild.leadingComments;
            }
        } else if (extra.leadingComments.length > 0 && extra.leadingComments[extra.leadingComments.length - 1].range[1] <= node.range[0]) {
            node.leadingComments = extra.leadingComments;
            extra.leadingComments = [];
        }

        if (trailingComments) {
            node.trailingComments = trailingComments;
        }

        bottomRight.push(node);
    }

    function markerApply(marker, node) {
        if (extra.range) {
            node.range = [marker.offset, index];
        }
        if (extra.loc) {
            node.loc = {
                start: {
                    line: marker.line,
                    column: marker.col
                },
                end: {
                    line: lineNumber,
                    column: index - lineStart
                }
            };
            node = delegate.postProcess(node);
        }
        if (extra.attachComment) {
            processComment(node);
        }
        return node;
    }

    SyntaxTreeDelegate = {

        name: 'SyntaxTree',

        postProcess: function (node) {
            return node;
        },

        createArrayExpression: function (elements) {
            return {
                type: Syntax.ArrayExpression,
                elements: elements
            };
        },

        createAssignmentExpression: function (operator, left, right) {
            return {
                type: Syntax.AssignmentExpression,
                operator: operator,
                left: left,
                right: right
            };
        },

        createBinaryExpression: function (operator, left, right) {
            var type = (operator === '||' || operator === '&&') ? Syntax.LogicalExpression :
                        Syntax.BinaryExpression;
            return {
                type: type,
                operator: operator,
                left: left,
                right: right
            };
        },

        createBlockStatement: function (body) {
            return {
                type: Syntax.BlockStatement,
                body: body
            };
        },

        createBreakStatement: function (label) {
            return {
                type: Syntax.BreakStatement,
                label: label
            };
        },

        createCallExpression: function (callee, args) {
            return {
                type: Syntax.CallExpression,
                callee: callee,
                'arguments': args
            };
        },

        createCatchClause: function (param, body) {
            return {
                type: Syntax.CatchClause,
                param: param,
                body: body
            };
        },

        createConditionalExpression: function (test, consequent, alternate) {
            return {
                type: Syntax.ConditionalExpression,
                test: test,
                consequent: consequent,
                alternate: alternate
            };
        },

        createContinueStatement: function (label) {
            return {
                type: Syntax.ContinueStatement,
                label: label
            };
        },

        createDebuggerStatement: function () {
            return {
                type: Syntax.DebuggerStatement
            };
        },

        createDoWhileStatement: function (body, test) {
            return {
                type: Syntax.DoWhileStatement,
                body: body,
                test: test
            };
        },

        createEmptyStatement: function () {
            return {
                type: Syntax.EmptyStatement
            };
        },

        createExpressionStatement: function (expression) {
            return {
                type: Syntax.ExpressionStatement,
                expression: expression
            };
        },

        createForStatement: function (init, test, update, body) {
            return {
                type: Syntax.ForStatement,
                init: init,
                test: test,
                update: update,
                body: body
            };
        },

        createForInStatement: function (left, right, body) {
            return {
                type: Syntax.ForInStatement,
                left: left,
                right: right,
                body: body,
                each: false
            };
        },

        createForOfStatement: function (left, right, body) {
            return {
                type: Syntax.ForOfStatement,
                left: left,
                right: right,
                body: body
            };
        },

        createFunctionDeclaration: function (id, params, defaults, body, rest, generator, expression,
                                             isAsync, returnType, parametricType) {
            var funDecl = {
                type: Syntax.FunctionDeclaration,
                id: id,
                params: params,
                defaults: defaults,
                body: body,
                rest: rest,
                generator: generator,
                expression: expression,
                returnType: returnType,
                parametricType: parametricType
            };

            if (isAsync) {
                funDecl.async = true;
            }

            return funDecl;
        },

        createFunctionExpression: function (id, params, defaults, body, rest, generator, expression,
                                            isAsync, returnType, parametricType) {
            var funExpr = {
                type: Syntax.FunctionExpression,
                id: id,
                params: params,
                defaults: defaults,
                body: body,
                rest: rest,
                generator: generator,
                expression: expression,
                returnType: returnType,
                parametricType: parametricType
            };

            if (isAsync) {
                funExpr.async = true;
            }

            return funExpr;
        },

        createIdentifier: function (name) {
            return {
                type: Syntax.Identifier,
                name: name,
                // Only here to initialize the shape of the object to ensure
                // that the 'typeAnnotation' key is ordered before others that
                // are added later (like 'loc' and 'range'). This just helps
                // keep the shape of Identifier nodes consistent with everything
                // else.
                typeAnnotation: undefined
            };
        },

        createTypeAnnotation: function (typeIdentifier, parametricType, params, returnType, nullable) {
            return {
                type: Syntax.TypeAnnotation,
                id: typeIdentifier,
                parametricType: parametricType,
                params: params,
                returnType: returnType,
                nullable: nullable
            };
        },

        createParametricTypeAnnotation: function (parametricTypes) {
            return {
                type: Syntax.ParametricTypeAnnotation,
                params: parametricTypes
            };
        },

        createVoidTypeAnnotation: function () {
            return {
                type: Syntax.VoidTypeAnnotation
            };
        },

        createObjectTypeAnnotation: function (properties, nullable) {
            return {
                type: Syntax.ObjectTypeAnnotation,
                properties: properties,
                nullable: nullable
            };
        },

        createTypeAnnotatedIdentifier: function (identifier, annotation, isOptionalParam) {
            return {
                type: Syntax.TypeAnnotatedIdentifier,
                id: identifier,
                annotation: annotation
            };
        },

        createOptionalParameter: function (identifier) {
            return {
                type: Syntax.OptionalParameter,
                id: identifier
            };
        },

        createXJSAttribute: function (name, value) {
            return {
                type: Syntax.XJSAttribute,
                name: name,
                value: value || null
            };
        },

        createXJSSpreadAttribute: function (argument) {
            return {
                type: Syntax.XJSSpreadAttribute,
                argument: argument
            };
        },

        createXJSIdentifier: function (name) {
            return {
                type: Syntax.XJSIdentifier,
                name: name
            };
        },

        createXJSNamespacedName: function (namespace, name) {
            return {
                type: Syntax.XJSNamespacedName,
                namespace: namespace,
                name: name
            };
        },

        createXJSMemberExpression: function (object, property) {
            return {
                type: Syntax.XJSMemberExpression,
                object: object,
                property: property
            };
        },

        createXJSElement: function (openingElement, closingElement, children) {
            return {
                type: Syntax.XJSElement,
                openingElement: openingElement,
                closingElement: closingElement,
                children: children
            };
        },

        createXJSEmptyExpression: function () {
            return {
                type: Syntax.XJSEmptyExpression
            };
        },

        createXJSExpressionContainer: function (expression) {
            return {
                type: Syntax.XJSExpressionContainer,
                expression: expression
            };
        },

        createXJSOpeningElement: function (name, attributes, selfClosing) {
            return {
                type: Syntax.XJSOpeningElement,
                name: name,
                selfClosing: selfClosing,
                attributes: attributes
            };
        },

        createXJSClosingElement: function (name) {
            return {
                type: Syntax.XJSClosingElement,
                name: name
            };
        },

        createIfStatement: function (test, consequent, alternate) {
            return {
                type: Syntax.IfStatement,
                test: test,
                consequent: consequent,
                alternate: alternate
            };
        },

        createLabeledStatement: function (label, body) {
            return {
                type: Syntax.LabeledStatement,
                label: label,
                body: body
            };
        },

        createLiteral: function (token) {
            var object = {
                type: Syntax.Literal,
                value: token.value,
                raw: source.slice(token.range[0], token.range[1])
            };
            if (token.regex) {
                object.regex = token.regex;
            }
            return object;
        },

        createMemberExpression: function (accessor, object, property) {
            return {
                type: Syntax.MemberExpression,
                computed: accessor === '[',
                object: object,
                property: property
            };
        },

        createNewExpression: function (callee, args) {
            return {
                type: Syntax.NewExpression,
                callee: callee,
                'arguments': args
            };
        },

        createObjectExpression: function (properties) {
            return {
                type: Syntax.ObjectExpression,
                properties: properties
            };
        },

        createPostfixExpression: function (operator, argument) {
            return {
                type: Syntax.UpdateExpression,
                operator: operator,
                argument: argument,
                prefix: false
            };
        },

        createProgram: function (body) {
            return {
                type: Syntax.Program,
                body: body
            };
        },

        createProperty: function (kind, key, value, method, shorthand, computed) {
            return {
                type: Syntax.Property,
                key: key,
                value: value,
                kind: kind,
                method: method,
                shorthand: shorthand,
                computed: computed
            };
        },

        createReturnStatement: function (argument) {
            return {
                type: Syntax.ReturnStatement,
                argument: argument
            };
        },

        createSequenceExpression: function (expressions) {
            return {
                type: Syntax.SequenceExpression,
                expressions: expressions
            };
        },

        createSwitchCase: function (test, consequent) {
            return {
                type: Syntax.SwitchCase,
                test: test,
                consequent: consequent
            };
        },

        createSwitchStatement: function (discriminant, cases) {
            return {
                type: Syntax.SwitchStatement,
                discriminant: discriminant,
                cases: cases
            };
        },

        createThisExpression: function () {
            return {
                type: Syntax.ThisExpression
            };
        },

        createThrowStatement: function (argument) {
            return {
                type: Syntax.ThrowStatement,
                argument: argument
            };
        },

        createTryStatement: function (block, guardedHandlers, handlers, finalizer) {
            return {
                type: Syntax.TryStatement,
                block: block,
                guardedHandlers: guardedHandlers,
                handlers: handlers,
                finalizer: finalizer
            };
        },

        createUnaryExpression: function (operator, argument) {
            if (operator === '++' || operator === '--') {
                return {
                    type: Syntax.UpdateExpression,
                    operator: operator,
                    argument: argument,
                    prefix: true
                };
            }
            return {
                type: Syntax.UnaryExpression,
                operator: operator,
                argument: argument,
                prefix: true
            };
        },

        createVariableDeclaration: function (declarations, kind) {
            return {
                type: Syntax.VariableDeclaration,
                declarations: declarations,
                kind: kind
            };
        },

        createVariableDeclarator: function (id, init) {
            return {
                type: Syntax.VariableDeclarator,
                id: id,
                init: init
            };
        },

        createWhileStatement: function (test, body) {
            return {
                type: Syntax.WhileStatement,
                test: test,
                body: body
            };
        },

        createWithStatement: function (object, body) {
            return {
                type: Syntax.WithStatement,
                object: object,
                body: body
            };
        },

        createTemplateElement: function (value, tail) {
            return {
                type: Syntax.TemplateElement,
                value: value,
                tail: tail
            };
        },

        createTemplateLiteral: function (quasis, expressions) {
            return {
                type: Syntax.TemplateLiteral,
                quasis: quasis,
                expressions: expressions
            };
        },

        createSpreadElement: function (argument) {
            return {
                type: Syntax.SpreadElement,
                argument: argument
            };
        },

        createSpreadProperty: function (argument) {
            return {
                type: Syntax.SpreadProperty,
                argument: argument
            };
        },

        createTaggedTemplateExpression: function (tag, quasi) {
            return {
                type: Syntax.TaggedTemplateExpression,
                tag: tag,
                quasi: quasi
            };
        },

        createArrowFunctionExpression: function (params, defaults, body, rest, expression, isAsync) {
            var arrowExpr = {
                type: Syntax.ArrowFunctionExpression,
                id: null,
                params: params,
                defaults: defaults,
                body: body,
                rest: rest,
                generator: false,
                expression: expression
            };

            if (isAsync) {
                arrowExpr.async = true;
            }

            return arrowExpr;
        },

        createMethodDefinition: function (propertyType, kind, key, value) {
            return {
                type: Syntax.MethodDefinition,
                key: key,
                value: value,
                kind: kind,
                'static': propertyType === ClassPropertyType.static
            };
        },

        createClassProperty: function (propertyIdentifier) {
            return {
                type: Syntax.ClassProperty,
                id: propertyIdentifier
            };
        },

        createClassBody: function (body) {
            return {
                type: Syntax.ClassBody,
                body: body
            };
        },

        createClassExpression: function (id, superClass, body, parametricType) {
            return {
                type: Syntax.ClassExpression,
                id: id,
                superClass: superClass,
                body: body,
                parametricType: parametricType
            };
        },

        createClassDeclaration: function (id, superClass, body, parametricType, superParametricType) {
            return {
                type: Syntax.ClassDeclaration,
                id: id,
                superClass: superClass,
                body: body,
                parametricType: parametricType,
                superParametricType: superParametricType
            };
        },

        createModuleSpecifier: function (token) {
            return {
                type: Syntax.ModuleSpecifier,
                value: token.value,
                raw: source.slice(token.range[0], token.range[1])
            };
        },

        createExportSpecifier: function (id, name) {
            return {
                type: Syntax.ExportSpecifier,
                id: id,
                name: name
            };
        },

        createExportBatchSpecifier: function () {
            return {
                type: Syntax.ExportBatchSpecifier
            };
        },

        createImportDefaultSpecifier: function (id) {
            return {
                type: Syntax.ImportDefaultSpecifier,
                id: id
            };
        },

        createImportNamespaceSpecifier: function (id) {
            return {
                type: Syntax.ImportNamespaceSpecifier,
                id: id
            };
        },

        createExportDeclaration: function (isDefault, declaration, specifiers, source) {
            return {
                type: Syntax.ExportDeclaration,
                'default': !!isDefault,
                declaration: declaration,
                specifiers: specifiers,
                source: source
            };
        },

        createImportSpecifier: function (id, name) {
            return {
                type: Syntax.ImportSpecifier,
                id: id,
                name: name
            };
        },

        createImportDeclaration: function (specifiers, source) {
            return {
                type: Syntax.ImportDeclaration,
                specifiers: specifiers,
                source: source
            };
        },

        createYieldExpression: function (argument, delegate) {
            return {
                type: Syntax.YieldExpression,
                argument: argument,
                delegate: delegate
            };
        },

        createAwaitExpression: function (argument) {
            return {
                type: Syntax.AwaitExpression,
                argument: argument
            };
        },

        createComprehensionExpression: function (filter, blocks, body) {
            return {
                type: Syntax.ComprehensionExpression,
                filter: filter,
                blocks: blocks,
                body: body
            };
        }

    };

    // Return true if there is a line terminator before the next token.

    function peekLineTerminator() {
        var pos, line, start, found;

        pos = index;
        line = lineNumber;
        start = lineStart;
        skipComment();
        found = lineNumber !== line;
        index = pos;
        lineNumber = line;
        lineStart = start;

        return found;
    }

    // Throw an exception

    function throwError(token, messageFormat) {
        var error,
            args = Array.prototype.slice.call(arguments, 2),
            msg = messageFormat.replace(
                /%(\d)/g,
                function (whole, index) {
                    assert(index < args.length, 'Message reference must be in range');
                    return args[index];
                }
            );

        if (typeof token.lineNumber === 'number') {
            error = new Error('Line ' + token.lineNumber + ': ' + msg);
            error.index = token.range[0];
            error.lineNumber = token.lineNumber;
            error.column = token.range[0] - lineStart + 1;
        } else {
            error = new Error('Line ' + lineNumber + ': ' + msg);
            error.index = index;
            error.lineNumber = lineNumber;
            error.column = index - lineStart + 1;
        }

        error.description = msg;
        throw error;
    }

    function throwErrorTolerant() {
        try {
            throwError.apply(null, arguments);
        } catch (e) {
            if (extra.errors) {
                extra.errors.push(e);
            } else {
                throw e;
            }
        }
    }


    // Throw an exception because of the token.

    function throwUnexpected(token) {
        if (token.type === Token.EOF) {
            throwError(token, Messages.UnexpectedEOS);
        }

        if (token.type === Token.NumericLiteral) {
            throwError(token, Messages.UnexpectedNumber);
        }

        if (token.type === Token.StringLiteral || token.type === Token.XJSText) {
            throwError(token, Messages.UnexpectedString);
        }

        if (token.type === Token.Identifier) {
            throwError(token, Messages.UnexpectedIdentifier);
        }

        if (token.type === Token.Keyword) {
            if (isFutureReservedWord(token.value)) {
                throwError(token, Messages.UnexpectedReserved);
            } else if (strict && isStrictModeReservedWord(token.value)) {
                throwErrorTolerant(token, Messages.StrictReservedWord);
                return;
            }
            throwError(token, Messages.UnexpectedToken, token.value);
        }

        if (token.type === Token.Template) {
            throwError(token, Messages.UnexpectedTemplate, token.value.raw);
        }

        // BooleanLiteral, NullLiteral, or Punctuator.
        throwError(token, Messages.UnexpectedToken, token.value);
    }

    // Expect the next token to match the specified punctuator.
    // If not, an exception will be thrown.

    function expect(value) {
        var token = lex();
        if (token.type !== Token.Punctuator || token.value !== value) {
            throwUnexpected(token);
        }
    }

    // Expect the next token to match the specified keyword.
    // If not, an exception will be thrown.

    function expectKeyword(keyword, contextual) {
        var token = lex();
        if (token.type !== (contextual ? Token.Identifier : Token.Keyword) ||
                token.value !== keyword) {
            throwUnexpected(token);
        }
    }

    // Expect the next token to match the specified contextual keyword.
    // If not, an exception will be thrown.

    function expectContextualKeyword(keyword) {
        return expectKeyword(keyword, true);
    }

    // Return true if the next token matches the specified punctuator.

    function match(value) {
        return lookahead.type === Token.Punctuator && lookahead.value === value;
    }

    // Return true if the next token matches the specified keyword

    function matchKeyword(keyword, contextual) {
        var expectedType = contextual ? Token.Identifier : Token.Keyword;
        return lookahead.type === expectedType && lookahead.value === keyword;
    }

    // Return true if the next token matches the specified contextual keyword

    function matchContextualKeyword(keyword) {
        return matchKeyword(keyword, true);
    }

    // Return true if the next token is an assignment operator

    function matchAssign() {
        var op;

        if (lookahead.type !== Token.Punctuator) {
            return false;
        }
        op = lookahead.value;
        return op === '=' ||
            op === '*=' ||
            op === '/=' ||
            op === '%=' ||
            op === '+=' ||
            op === '-=' ||
            op === '<<=' ||
            op === '>>=' ||
            op === '>>>=' ||
            op === '&=' ||
            op === '^=' ||
            op === '|=';
    }

    // Note that 'yield' is treated as a keyword in strict mode, but a
    // contextual keyword (identifier) in non-strict mode, so we need to
    // use matchKeyword('yield', false) and matchKeyword('yield', true)
    // (i.e. matchContextualKeyword) appropriately.
    function matchYield() {
        return state.yieldAllowed && matchKeyword('yield', !strict);
    }

    function matchAsync() {
        var backtrackToken = lookahead, matches = false;

        if (matchContextualKeyword('async')) {
            lex(); // Make sure peekLineTerminator() starts after 'async'.
            matches = !peekLineTerminator();
            rewind(backtrackToken); // Revert the lex().
        }

        return matches;
    }

    function matchAwait() {
        return state.awaitAllowed && matchContextualKeyword('await');
    }

    function consumeSemicolon() {
        var line, oldIndex = index, oldLineNumber = lineNumber,
            oldLineStart = lineStart, oldLookahead = lookahead;

        // Catch the very common case first: immediately a semicolon (char #59).
        if (source.charCodeAt(index) === 59) {
            lex();
            return;
        }

        line = lineNumber;
        skipComment();
        if (lineNumber !== line) {
            index = oldIndex;
            lineNumber = oldLineNumber;
            lineStart = oldLineStart;
            lookahead = oldLookahead;
            return;
        }

        if (match(';')) {
            lex();
            return;
        }

        if (lookahead.type !== Token.EOF && !match('}')) {
            throwUnexpected(lookahead);
        }
    }

    // Return true if provided expression is LeftHandSideExpression

    function isLeftHandSide(expr) {
        return expr.type === Syntax.Identifier || expr.type === Syntax.MemberExpression;
    }

    function isAssignableLeftHandSide(expr) {
        return isLeftHandSide(expr) || expr.type === Syntax.ObjectPattern || expr.type === Syntax.ArrayPattern;
    }

    // 11.1.4 Array Initialiser

    function parseArrayInitialiser() {
        var elements = [], blocks = [], filter = null, tmp, possiblecomprehension = true, body,
            marker = markerCreate();

        expect('[');
        while (!match(']')) {
            if (lookahead.value === 'for' &&
                    lookahead.type === Token.Keyword) {
                if (!possiblecomprehension) {
                    throwError({}, Messages.ComprehensionError);
                }
                matchKeyword('for');
                tmp = parseForStatement({ignoreBody: true});
                tmp.of = tmp.type === Syntax.ForOfStatement;
                tmp.type = Syntax.ComprehensionBlock;
                if (tmp.left.kind) { // can't be let or const
                    throwError({}, Messages.ComprehensionError);
                }
                blocks.push(tmp);
            } else if (lookahead.value === 'if' &&
                           lookahead.type === Token.Keyword) {
                if (!possiblecomprehension) {
                    throwError({}, Messages.ComprehensionError);
                }
                expectKeyword('if');
                expect('(');
                filter = parseExpression();
                expect(')');
            } else if (lookahead.value === ',' &&
                           lookahead.type === Token.Punctuator) {
                possiblecomprehension = false; // no longer allowed.
                lex();
                elements.push(null);
            } else {
                tmp = parseSpreadOrAssignmentExpression();
                elements.push(tmp);
                if (tmp && tmp.type === Syntax.SpreadElement) {
                    if (!match(']')) {
                        throwError({}, Messages.ElementAfterSpreadElement);
                    }
                } else if (!(match(']') || matchKeyword('for') || matchKeyword('if'))) {
                    expect(','); // this lexes.
                    possiblecomprehension = false;
                }
            }
        }

        expect(']');

        if (filter && !blocks.length) {
            throwError({}, Messages.ComprehensionRequiresBlock);
        }

        if (blocks.length) {
            if (elements.length !== 1) {
                throwError({}, Messages.ComprehensionError);
            }
            return markerApply(marker, delegate.createComprehensionExpression(filter, blocks, elements[0]));
        }
        return markerApply(marker, delegate.createArrayExpression(elements));
    }

    // 11.1.5 Object Initialiser

    function parsePropertyFunction(options) {
        var previousStrict, previousYieldAllowed, previousAwaitAllowed,
            params, defaults, body, marker = markerCreate();

        previousStrict = strict;
        previousYieldAllowed = state.yieldAllowed;
        state.yieldAllowed = options.generator;
        previousAwaitAllowed = state.awaitAllowed;
        state.awaitAllowed = options.async;
        params = options.params || [];
        defaults = options.defaults || [];

        body = parseConciseBody();
        if (options.name && strict && isRestrictedWord(params[0].name)) {
            throwErrorTolerant(options.name, Messages.StrictParamName);
        }
        strict = previousStrict;
        state.yieldAllowed = previousYieldAllowed;
        state.awaitAllowed = previousAwaitAllowed;

        return markerApply(marker, delegate.createFunctionExpression(
            null,
            params,
            defaults,
            body,
            options.rest || null,
            options.generator,
            body.type !== Syntax.BlockStatement,
            options.async,
            options.returnType,
            options.parametricType
        ));
    }


    function parsePropertyMethodFunction(options) {
        var previousStrict, tmp, method;

        previousStrict = strict;
        strict = true;

        tmp = parseParams();

        if (tmp.stricted) {
            throwErrorTolerant(tmp.stricted, tmp.message);
        }

        method = parsePropertyFunction({
            params: tmp.params,
            defaults: tmp.defaults,
            rest: tmp.rest,
            generator: options.generator,
            async: options.async,
            returnType: tmp.returnType,
            parametricType: options.parametricType
        });

        strict = previousStrict;

        return method;
    }


    function parseObjectPropertyKey() {
        var marker = markerCreate(),
            token = lex(),
            propertyKey,
            result;

        // Note: This function is called only from parseObjectProperty(), where
        // EOF and Punctuator tokens are already filtered out.

        if (token.type === Token.StringLiteral || token.type === Token.NumericLiteral) {
            if (strict && token.octal) {
                throwErrorTolerant(token, Messages.StrictOctalLiteral);
            }
            return markerApply(marker, delegate.createLiteral(token));
        }

        if (token.type === Token.Punctuator && token.value === '[') {
            // For computed properties we should skip the [ and ], and
            // capture in marker only the assignment expression itself.
            marker = markerCreate();
            propertyKey = parseAssignmentExpression();
            result = markerApply(marker, propertyKey);
            expect(']');
            return result;
        }

        return markerApply(marker, delegate.createIdentifier(token.value));
    }

    function parseObjectProperty() {
        var token, key, id, value, param, expr, computed,
            marker = markerCreate();

        token = lookahead;
        computed = (token.value === '[');

        if (token.type === Token.Identifier || computed || matchAsync()) {
            id = parseObjectPropertyKey();

            if (match(':')) {
                lex();

                return markerApply(
                    marker,
                    delegate.createProperty(
                        'init',
                        id,
                        parseAssignmentExpression(),
                        false,
                        false,
                        computed
                    )
                );
            }

            if (match('(')) {
                return markerApply(
                    marker,
                    delegate.createProperty(
                        'init',
                        id,
                        parsePropertyMethodFunction({
                            generator: false,
                            async: false
                        }),
                        true,
                        false,
                        computed
                    )
                );
            }

            // Property Assignment: Getter and Setter.

            if (token.value === 'get') {
                computed = (lookahead.value === '[');
                key = parseObjectPropertyKey();

                expect('(');
                expect(')');

                return markerApply(
                    marker,
                    delegate.createProperty(
                        'get',
                        key,
                        parsePropertyFunction({
                            generator: false,
                            async: false
                        }),
                        false,
                        false,
                        computed
                    )
                );
            }

            if (token.value === 'set') {
                computed = (lookahead.value === '[');
                key = parseObjectPropertyKey();

                expect('(');
                token = lookahead;
                param = [ parseTypeAnnotatableIdentifier() ];
                expect(')');

                return markerApply(
                    marker,
                    delegate.createProperty(
                        'set',
                        key,
                        parsePropertyFunction({
                            params: param,
                            generator: false,
                            async: false,
                            name: token
                        }),
                        false,
                        false,
                        computed
                    )
                );
            }

            if (token.value === 'async') {
                computed = (lookahead.value === '[');
                key = parseObjectPropertyKey();

                return markerApply(
                    marker,
                    delegate.createProperty(
                        'init',
                        key,
                        parsePropertyMethodFunction({
                            generator: false,
                            async: true
                        }),
                        true,
                        false,
                        computed
                    )
                );
            }

            if (computed) {
                // Computed properties can only be used with full notation.
                throwUnexpected(lookahead);
            }

            return markerApply(
                marker,
                delegate.createProperty('init', id, id, false, true, false)
            );
        }

        if (token.type === Token.EOF || token.type === Token.Punctuator) {
            if (!match('*')) {
                throwUnexpected(token);
            }
            lex();

            computed = (lookahead.type === Token.Punctuator && lookahead.value === '[');

            id = parseObjectPropertyKey();

            if (!match('(')) {
                throwUnexpected(lex());
            }

            return markerApply(marker, delegate.createProperty('init', id, parsePropertyMethodFunction({ generator: true }), true, false, computed));
        }
        key = parseObjectPropertyKey();
        if (match(':')) {
            lex();
            return markerApply(marker, delegate.createProperty('init', key, parseAssignmentExpression(), false, false, false));
        }
        if (match('(')) {
            return markerApply(marker, delegate.createProperty('init', key, parsePropertyMethodFunction({ generator: false }), true, false, false));
        }
        throwUnexpected(lex());
    }

    function parseObjectSpreadProperty() {
        var marker = markerCreate();
        expect('...');
        return markerApply(marker, delegate.createSpreadProperty(parseAssignmentExpression()));
    }

    function parseObjectInitialiser() {
        var properties = [], property, name, key, kind, map = {}, toString = String,
            marker = markerCreate();

        expect('{');

        while (!match('}')) {
            if (match('...')) {
                property = parseObjectSpreadProperty();
            } else {
                property = parseObjectProperty();

                if (property.key.type === Syntax.Identifier) {
                    name = property.key.name;
                } else {
                    name = toString(property.key.value);
                }
                kind = (property.kind === 'init') ? PropertyKind.Data : (property.kind === 'get') ? PropertyKind.Get : PropertyKind.Set;

                key = '$' + name;
                if (Object.prototype.hasOwnProperty.call(map, key)) {
                    if (map[key] === PropertyKind.Data) {
                        if (strict && kind === PropertyKind.Data) {
                            throwErrorTolerant({}, Messages.StrictDuplicateProperty);
                        } else if (kind !== PropertyKind.Data) {
                            throwErrorTolerant({}, Messages.AccessorDataProperty);
                        }
                    } else {
                        if (kind === PropertyKind.Data) {
                            throwErrorTolerant({}, Messages.AccessorDataProperty);
                        } else if (map[key] & kind) {
                            throwErrorTolerant({}, Messages.AccessorGetSet);
                        }
                    }
                    map[key] |= kind;
                } else {
                    map[key] = kind;
                }
            }

            properties.push(property);

            if (!match('}')) {
                expect(',');
            }
        }

        expect('}');

        return markerApply(marker, delegate.createObjectExpression(properties));
    }

    function parseTemplateElement(option) {
        var marker = markerCreate(),
            token = scanTemplateElement(option);
        if (strict && token.octal) {
            throwError(token, Messages.StrictOctalLiteral);
        }
        return markerApply(marker, delegate.createTemplateElement({ raw: token.value.raw, cooked: token.value.cooked }, token.tail));
    }

    function parseTemplateLiteral() {
        var quasi, quasis, expressions, marker = markerCreate();

        quasi = parseTemplateElement({ head: true });
        quasis = [ quasi ];
        expressions = [];

        while (!quasi.tail) {
            expressions.push(parseExpression());
            quasi = parseTemplateElement({ head: false });
            quasis.push(quasi);
        }

        return markerApply(marker, delegate.createTemplateLiteral(quasis, expressions));
    }

    // 11.1.6 The Grouping Operator

    function parseGroupExpression() {
        var expr;

        expect('(');

        ++state.parenthesizedCount;

        expr = parseExpression();

        expect(')');

        return expr;
    }

    function matchAsyncFuncExprOrDecl() {
        var token;

        if (matchAsync()) {
            token = lookahead2();
            if (token.type === Token.Keyword && token.value === 'function') {
                return true;
            }
        }

        return false;
    }

    // 11.1 Primary Expressions

    function parsePrimaryExpression() {
        var marker, type, token, expr;

        type = lookahead.type;

        if (type === Token.Identifier) {
            marker = markerCreate();
            return markerApply(marker, delegate.createIdentifier(lex().value));
        }

        if (type === Token.StringLiteral || type === Token.NumericLiteral) {
            if (strict && lookahead.octal) {
                throwErrorTolerant(lookahead, Messages.StrictOctalLiteral);
            }
            marker = markerCreate();
            return markerApply(marker, delegate.createLiteral(lex()));
        }

        if (type === Token.Keyword) {
            if (matchKeyword('this')) {
                marker = markerCreate();
                lex();
                return markerApply(marker, delegate.createThisExpression());
            }

            if (matchKeyword('function')) {
                return parseFunctionExpression();
            }

            if (matchKeyword('class')) {
                return parseClassExpression();
            }

            if (matchKeyword('super')) {
                marker = markerCreate();
                lex();
                return markerApply(marker, delegate.createIdentifier('super'));
            }
        }

        if (type === Token.BooleanLiteral) {
            marker = markerCreate();
            token = lex();
            token.value = (token.value === 'true');
            return markerApply(marker, delegate.createLiteral(token));
        }

        if (type === Token.NullLiteral) {
            marker = markerCreate();
            token = lex();
            token.value = null;
            return markerApply(marker, delegate.createLiteral(token));
        }

        if (match('[')) {
            return parseArrayInitialiser();
        }

        if (match('{')) {
            return parseObjectInitialiser();
        }

        if (match('(')) {
            return parseGroupExpression();
        }

        if (match('/') || match('/=')) {
            marker = markerCreate();
            return markerApply(marker, delegate.createLiteral(scanRegExp()));
        }

        if (type === Token.Template) {
            return parseTemplateLiteral();
        }

        if (match('<')) {
            return parseXJSElement();
        }

        throwUnexpected(lex());
    }

    // 11.2 Left-Hand-Side Expressions

    function parseArguments() {
        var args = [], arg;

        expect('(');

        if (!match(')')) {
            while (index < length) {
                arg = parseSpreadOrAssignmentExpression();
                args.push(arg);

                if (match(')')) {
                    break;
                } else if (arg.type === Syntax.SpreadElement) {
                    throwError({}, Messages.ElementAfterSpreadElement);
                }

                expect(',');
            }
        }

        expect(')');

        return args;
    }

    function parseSpreadOrAssignmentExpression() {
        if (match('...')) {
            var marker = markerCreate();
            lex();
            return markerApply(marker, delegate.createSpreadElement(parseAssignmentExpression()));
        }
        return parseAssignmentExpression();
    }

    function parseNonComputedProperty() {
        var marker = markerCreate(),
            token = lex();

        if (!isIdentifierName(token)) {
            throwUnexpected(token);
        }

        return markerApply(marker, delegate.createIdentifier(token.value));
    }

    function parseNonComputedMember() {
        expect('.');

        return parseNonComputedProperty();
    }

    function parseComputedMember() {
        var expr;

        expect('[');

        expr = parseExpression();

        expect(']');

        return expr;
    }

    function parseNewExpression() {
        var callee, args, marker = markerCreate();

        expectKeyword('new');
        callee = parseLeftHandSideExpression();
        args = match('(') ? parseArguments() : [];

        return markerApply(marker, delegate.createNewExpression(callee, args));
    }

    function parseLeftHandSideExpressionAllowCall() {
        var expr, args, marker = markerCreate();

        expr = matchKeyword('new') ? parseNewExpression() : parsePrimaryExpression();

        while (match('.') || match('[') || match('(') || lookahead.type === Token.Template) {
            if (match('(')) {
                args = parseArguments();
                expr = markerApply(marker, delegate.createCallExpression(expr, args));
            } else if (match('[')) {
                expr = markerApply(marker, delegate.createMemberExpression('[', expr, parseComputedMember()));
            } else if (match('.')) {
                expr = markerApply(marker, delegate.createMemberExpression('.', expr, parseNonComputedMember()));
            } else {
                expr = markerApply(marker, delegate.createTaggedTemplateExpression(expr, parseTemplateLiteral()));
            }
        }

        return expr;
    }

    function parseLeftHandSideExpression() {
        var expr, marker = markerCreate();

        expr = matchKeyword('new') ? parseNewExpression() : parsePrimaryExpression();

        while (match('.') || match('[') || lookahead.type === Token.Template) {
            if (match('[')) {
                expr = markerApply(marker, delegate.createMemberExpression('[', expr, parseComputedMember()));
            } else if (match('.')) {
                expr = markerApply(marker, delegate.createMemberExpression('.', expr, parseNonComputedMember()));
            } else {
                expr = markerApply(marker, delegate.createTaggedTemplateExpression(expr, parseTemplateLiteral()));
            }
        }

        return expr;
    }

    // 11.3 Postfix Expressions

    function parsePostfixExpression() {
        var marker = markerCreate(),
            expr = parseLeftHandSideExpressionAllowCall(),
            token;

        if (lookahead.type !== Token.Punctuator) {
            return expr;
        }

        if ((match('++') || match('--')) && !peekLineTerminator()) {
            // 11.3.1, 11.3.2
            if (strict && expr.type === Syntax.Identifier && isRestrictedWord(expr.name)) {
                throwErrorTolerant({}, Messages.StrictLHSPostfix);
            }

            if (!isLeftHandSide(expr)) {
                throwError({}, Messages.InvalidLHSInAssignment);
            }

            token = lex();
            expr = markerApply(marker, delegate.createPostfixExpression(token.value, expr));
        }

        return expr;
    }

    // 11.4 Unary Operators

    function parseUnaryExpression() {
        var marker, token, expr;

        if (lookahead.type !== Token.Punctuator && lookahead.type !== Token.Keyword) {
            return parsePostfixExpression();
        }

        if (match('++') || match('--')) {
            marker = markerCreate();
            token = lex();
            expr = parseUnaryExpression();
            // 11.4.4, 11.4.5
            if (strict && expr.type === Syntax.Identifier && isRestrictedWord(expr.name)) {
                throwErrorTolerant({}, Messages.StrictLHSPrefix);
            }

            if (!isLeftHandSide(expr)) {
                throwError({}, Messages.InvalidLHSInAssignment);
            }

            return markerApply(marker, delegate.createUnaryExpression(token.value, expr));
        }

        if (match('+') || match('-') || match('~') || match('!')) {
            marker = markerCreate();
            token = lex();
            expr = parseUnaryExpression();
            return markerApply(marker, delegate.createUnaryExpression(token.value, expr));
        }

        if (matchKeyword('delete') || matchKeyword('void') || matchKeyword('typeof')) {
            marker = markerCreate();
            token = lex();
            expr = parseUnaryExpression();
            expr = markerApply(marker, delegate.createUnaryExpression(token.value, expr));
            if (strict && expr.operator === 'delete' && expr.argument.type === Syntax.Identifier) {
                throwErrorTolerant({}, Messages.StrictDelete);
            }
            return expr;
        }

        return parsePostfixExpression();
    }

    function binaryPrecedence(token, allowIn) {
        var prec = 0;

        if (token.type !== Token.Punctuator && token.type !== Token.Keyword) {
            return 0;
        }

        switch (token.value) {
        case '||':
            prec = 1;
            break;

        case '&&':
            prec = 2;
            break;

        case '|':
            prec = 3;
            break;

        case '^':
            prec = 4;
            break;

        case '&':
            prec = 5;
            break;

        case '==':
        case '!=':
        case '===':
        case '!==':
            prec = 6;
            break;

        case '<':
        case '>':
        case '<=':
        case '>=':
        case 'instanceof':
            prec = 7;
            break;

        case 'in':
            prec = allowIn ? 7 : 0;
            break;

        case '<<':
        case '>>':
        case '>>>':
            prec = 8;
            break;

        case '+':
        case '-':
            prec = 9;
            break;

        case '*':
        case '/':
        case '%':
            prec = 11;
            break;

        default:
            break;
        }

        return prec;
    }

    // 11.5 Multiplicative Operators
    // 11.6 Additive Operators
    // 11.7 Bitwise Shift Operators
    // 11.8 Relational Operators
    // 11.9 Equality Operators
    // 11.10 Binary Bitwise Operators
    // 11.11 Binary Logical Operators

    function parseBinaryExpression() {
        var expr, token, prec, previousAllowIn, stack, right, operator, left, i,
            marker, markers;

        previousAllowIn = state.allowIn;
        state.allowIn = true;

        marker = markerCreate();
        left = parseUnaryExpression();

        token = lookahead;
        prec = binaryPrecedence(token, previousAllowIn);
        if (prec === 0) {
            return left;
        }
        token.prec = prec;
        lex();

        markers = [marker, markerCreate()];
        right = parseUnaryExpression();

        stack = [left, token, right];

        while ((prec = binaryPrecedence(lookahead, previousAllowIn)) > 0) {

            // Reduce: make a binary expression from the three topmost entries.
            while ((stack.length > 2) && (prec <= stack[stack.length - 2].prec)) {
                right = stack.pop();
                operator = stack.pop().value;
                left = stack.pop();
                expr = delegate.createBinaryExpression(operator, left, right);
                markers.pop();
                marker = markers.pop();
                markerApply(marker, expr);
                stack.push(expr);
                markers.push(marker);
            }

            // Shift.
            token = lex();
            token.prec = prec;
            stack.push(token);
            markers.push(markerCreate());
            expr = parseUnaryExpression();
            stack.push(expr);
        }

        state.allowIn = previousAllowIn;

        // Final reduce to clean-up the stack.
        i = stack.length - 1;
        expr = stack[i];
        markers.pop();
        while (i > 1) {
            expr = delegate.createBinaryExpression(stack[i - 1].value, stack[i - 2], expr);
            i -= 2;
            marker = markers.pop();
            markerApply(marker, expr);
        }

        return expr;
    }


    // 11.12 Conditional Operator

    function parseConditionalExpression() {
        var expr, previousAllowIn, consequent, alternate, marker = markerCreate();
        expr = parseBinaryExpression();

        if (match('?')) {
            lex();
            previousAllowIn = state.allowIn;
            state.allowIn = true;
            consequent = parseAssignmentExpression();
            state.allowIn = previousAllowIn;
            expect(':');
            alternate = parseAssignmentExpression();

            expr = markerApply(marker, delegate.createConditionalExpression(expr, consequent, alternate));
        }

        return expr;
    }

    // 11.13 Assignment Operators

    function reinterpretAsAssignmentBindingPattern(expr) {
        var i, len, property, element;

        if (expr.type === Syntax.ObjectExpression) {
            expr.type = Syntax.ObjectPattern;
            for (i = 0, len = expr.properties.length; i < len; i += 1) {
                property = expr.properties[i];
                if (property.type === Syntax.SpreadProperty) {
                    if (i < len - 1) {
                        throwError({}, Messages.PropertyAfterSpreadProperty);
                    }
                    reinterpretAsAssignmentBindingPattern(property.argument);
                } else {
                    if (property.kind !== 'init') {
                        throwError({}, Messages.InvalidLHSInAssignment);
                    }
                    reinterpretAsAssignmentBindingPattern(property.value);
                }
            }
        } else if (expr.type === Syntax.ArrayExpression) {
            expr.type = Syntax.ArrayPattern;
            for (i = 0, len = expr.elements.length; i < len; i += 1) {
                element = expr.elements[i];
                if (element) {
                    reinterpretAsAssignmentBindingPattern(element);
                }
            }
        } else if (expr.type === Syntax.Identifier) {
            if (isRestrictedWord(expr.name)) {
                throwError({}, Messages.InvalidLHSInAssignment);
            }
        } else if (expr.type === Syntax.SpreadElement) {
            reinterpretAsAssignmentBindingPattern(expr.argument);
            if (expr.argument.type === Syntax.ObjectPattern) {
                throwError({}, Messages.ObjectPatternAsSpread);
            }
        } else {
            if (expr.type !== Syntax.MemberExpression && expr.type !== Syntax.CallExpression && expr.type !== Syntax.NewExpression) {
                throwError({}, Messages.InvalidLHSInAssignment);
            }
        }
    }


    function reinterpretAsDestructuredParameter(options, expr) {
        var i, len, property, element;

        if (expr.type === Syntax.ObjectExpression) {
            expr.type = Syntax.ObjectPattern;
            for (i = 0, len = expr.properties.length; i < len; i += 1) {
                property = expr.properties[i];
                if (property.type === Syntax.SpreadProperty) {
                    if (i < len - 1) {
                        throwError({}, Messages.PropertyAfterSpreadProperty);
                    }
                    reinterpretAsDestructuredParameter(options, property.argument);
                } else {
                    if (property.kind !== 'init') {
                        throwError({}, Messages.InvalidLHSInFormalsList);
                    }
                    reinterpretAsDestructuredParameter(options, property.value);
                }
            }
        } else if (expr.type === Syntax.ArrayExpression) {
            expr.type = Syntax.ArrayPattern;
            for (i = 0, len = expr.elements.length; i < len; i += 1) {
                element = expr.elements[i];
                if (element) {
                    reinterpretAsDestructuredParameter(options, element);
                }
            }
        } else if (expr.type === Syntax.Identifier) {
            validateParam(options, expr, expr.name);
        } else {
            if (expr.type !== Syntax.MemberExpression) {
                throwError({}, Messages.InvalidLHSInFormalsList);
            }
        }
    }

    function reinterpretAsCoverFormalsList(expressions) {
        var i, len, param, params, defaults, defaultCount, options, rest;

        params = [];
        defaults = [];
        defaultCount = 0;
        rest = null;
        options = {
            paramSet: {}
        };

        for (i = 0, len = expressions.length; i < len; i += 1) {
            param = expressions[i];
            if (param.type === Syntax.Identifier) {
                params.push(param);
                defaults.push(null);
                validateParam(options, param, param.name);
            } else if (param.type === Syntax.ObjectExpression || param.type === Syntax.ArrayExpression) {
                reinterpretAsDestructuredParameter(options, param);
                params.push(param);
                defaults.push(null);
            } else if (param.type === Syntax.SpreadElement) {
                assert(i === len - 1, 'It is guaranteed that SpreadElement is last element by parseExpression');
                reinterpretAsDestructuredParameter(options, param.argument);
                rest = param.argument;
            } else if (param.type === Syntax.AssignmentExpression) {
                params.push(param.left);
                defaults.push(param.right);
                ++defaultCount;
                validateParam(options, param.left, param.left.name);
            } else {
                return null;
            }
        }

        if (options.message === Messages.StrictParamDupe) {
            throwError(
                strict ? options.stricted : options.firstRestricted,
                options.message
            );
        }

        if (defaultCount === 0) {
            defaults = [];
        }

        return {
            params: params,
            defaults: defaults,
            rest: rest,
            stricted: options.stricted,
            firstRestricted: options.firstRestricted,
            message: options.message
        };
    }

    function parseArrowFunctionExpression(options, marker) {
        var previousStrict, previousYieldAllowed, previousAwaitAllowed, body;

        expect('=>');

        previousStrict = strict;
        previousYieldAllowed = state.yieldAllowed;
        state.yieldAllowed = false;
        previousAwaitAllowed = state.awaitAllowed;
        state.awaitAllowed = !!options.async;
        body = parseConciseBody();

        if (strict && options.firstRestricted) {
            throwError(options.firstRestricted, options.message);
        }
        if (strict && options.stricted) {
            throwErrorTolerant(options.stricted, options.message);
        }

        strict = previousStrict;
        state.yieldAllowed = previousYieldAllowed;
        state.awaitAllowed = previousAwaitAllowed;

        return markerApply(marker, delegate.createArrowFunctionExpression(
            options.params,
            options.defaults,
            body,
            options.rest,
            body.type !== Syntax.BlockStatement,
            !!options.async
        ));
    }

    function parseAssignmentExpression() {
        var marker, expr, token, params, oldParenthesizedCount,
            backtrackToken = lookahead, possiblyAsync = false;

        if (matchYield()) {
            return parseYieldExpression();
        }

        if (matchAwait()) {
            return parseAwaitExpression();
        }

        oldParenthesizedCount = state.parenthesizedCount;

        marker = markerCreate();

        if (matchAsyncFuncExprOrDecl()) {
            return parseFunctionExpression();
        }

        if (matchAsync()) {
            // We can't be completely sure that this 'async' token is
            // actually a contextual keyword modifying a function
            // expression, so we might have to un-lex() it later by
            // calling rewind(backtrackToken).
            possiblyAsync = true;
            lex();
        }

        if (match('(')) {
            token = lookahead2();
            if ((token.type === Token.Punctuator && token.value === ')') || token.value === '...') {
                params = parseParams();
                if (!match('=>')) {
                    throwUnexpected(lex());
                }
                params.async = possiblyAsync;
                return parseArrowFunctionExpression(params, marker);
            }
        }

        token = lookahead;

        // If the 'async' keyword is not followed by a '(' character or an
        // identifier, then it can't be an arrow function modifier, and we
        // should interpret it as a normal identifer.
        if (possiblyAsync && !match('(') && token.type !== Token.Identifier) {
            possiblyAsync = false;
            rewind(backtrackToken);
        }

        expr = parseConditionalExpression();

        if (match('=>') &&
                (state.parenthesizedCount === oldParenthesizedCount ||
                state.parenthesizedCount === (oldParenthesizedCount + 1))) {
            if (expr.type === Syntax.Identifier) {
                params = reinterpretAsCoverFormalsList([ expr ]);
            } else if (expr.type === Syntax.SequenceExpression) {
                params = reinterpretAsCoverFormalsList(expr.expressions);
            }
            if (params) {
                params.async = possiblyAsync;
                return parseArrowFunctionExpression(params, marker);
            }
        }

        // If we haven't returned by now, then the 'async' keyword was not
        // a function modifier, and we should rewind and interpret it as a
        // normal identifier.
        if (possiblyAsync) {
            possiblyAsync = false;
            rewind(backtrackToken);
            expr = parseConditionalExpression();
        }

        if (matchAssign()) {
            // 11.13.1
            if (strict && expr.type === Syntax.Identifier && isRestrictedWord(expr.name)) {
                throwErrorTolerant(token, Messages.StrictLHSAssignment);
            }

            // ES.next draf 11.13 Runtime Semantics step 1
            if (match('=') && (expr.type === Syntax.ObjectExpression || expr.type === Syntax.ArrayExpression)) {
                reinterpretAsAssignmentBindingPattern(expr);
            } else if (!isLeftHandSide(expr)) {
                throwError({}, Messages.InvalidLHSInAssignment);
            }

            expr = markerApply(marker, delegate.createAssignmentExpression(lex().value, expr, parseAssignmentExpression()));
        }

        return expr;
    }

    // 11.14 Comma Operator

    function parseExpression() {
        var marker, expr, expressions, sequence, coverFormalsList, spreadFound, oldParenthesizedCount;

        oldParenthesizedCount = state.parenthesizedCount;

        marker = markerCreate();
        expr = parseAssignmentExpression();
        expressions = [ expr ];

        if (match(',')) {
            while (index < length) {
                if (!match(',')) {
                    break;
                }

                lex();
                expr = parseSpreadOrAssignmentExpression();
                expressions.push(expr);

                if (expr.type === Syntax.SpreadElement) {
                    spreadFound = true;
                    if (!match(')')) {
                        throwError({}, Messages.ElementAfterSpreadElement);
                    }
                    break;
                }
            }

            sequence = markerApply(marker, delegate.createSequenceExpression(expressions));
        }

        if (match('=>')) {
            // Do not allow nested parentheses on the LHS of the =>.
            if (state.parenthesizedCount === oldParenthesizedCount || state.parenthesizedCount === (oldParenthesizedCount + 1)) {
                expr = expr.type === Syntax.SequenceExpression ? expr.expressions : expressions;
                coverFormalsList = reinterpretAsCoverFormalsList(expr);
                if (coverFormalsList) {
                    return parseArrowFunctionExpression(coverFormalsList, marker);
                }
            }
            throwUnexpected(lex());
        }

        if (spreadFound && lookahead2().value !== '=>') {
            throwError({}, Messages.IllegalSpread);
        }

        return sequence || expr;
    }

    // 12.1 Block

    function parseStatementList() {
        var list = [],
            statement;

        while (index < length) {
            if (match('}')) {
                break;
            }
            statement = parseSourceElement();
            if (typeof statement === 'undefined') {
                break;
            }
            list.push(statement);
        }

        return list;
    }

    function parseBlock() {
        var block, marker = markerCreate();

        expect('{');

        block = parseStatementList();

        expect('}');

        return markerApply(marker, delegate.createBlockStatement(block));
    }

    // 12.2 Variable Statement

    function parseObjectTypeAnnotation(nullable) {
        var isMethod, marker, properties = [], property, propertyKey,
            propertyTypeAnnotation;

        expect('{');

        while (!match('}')) {
            marker = markerCreate();
            propertyKey = parseObjectPropertyKey();
            isMethod = match('(');
            propertyTypeAnnotation = parseTypeAnnotation();
            properties.push(markerApply(marker, delegate.createProperty(
                'init',
                propertyKey,
                propertyTypeAnnotation,
                isMethod,
                false
            )));

            if (!match('}')) {
                if (match(',') || match(';')) {
                    lex();
                } else {
                    throwUnexpected(lookahead);
                }
            }
        }

        expect('}');

        return delegate.createObjectTypeAnnotation(properties, nullable);
    }

    function parseVoidTypeAnnotation() {
        var marker = markerCreate();
        expectKeyword('void');
        return markerApply(marker, delegate.createVoidTypeAnnotation());
    }

    function parseParametricTypeAnnotation() {
        var marker = markerCreate(), typeIdentifier, paramTypes = [];

        expect('<');
        while (!match('>')) {
            paramTypes.push(parseVariableIdentifier());
            if (!match('>')) {
                expect(',');
            }
        }
        expect('>');

        return markerApply(marker, delegate.createParametricTypeAnnotation(
            paramTypes
        ));
    }

    function parseTypeAnnotation(dontExpectColon) {
        var typeIdentifier = null, params = null, returnType = null,
            nullable = false, marker = markerCreate(), returnTypeMarker = null,
            parametricType, annotation;

        if (!dontExpectColon) {
            expect(':');
        }

        if (match('?')) {
            lex();
            nullable = true;
        }

        if (match('{')) {
            return markerApply(marker, parseObjectTypeAnnotation(nullable));
        }

        if (lookahead.type === Token.Identifier) {
            typeIdentifier = parseVariableIdentifier();
            if (match('<')) {
                parametricType = parseParametricTypeAnnotation();
            }
        } else if (match('(')) {
            lex();
            params = [];
            while (lookahead.type === Token.Identifier || match('?')) {
                params.push(parseTypeAnnotatableIdentifier(
                    true, /* requireTypeAnnotation */
                    true /* canBeOptionalParam */
                ));
                if (!match(')')) {
                    expect(',');
                }
            }
            expect(')');

            returnTypeMarker = markerCreate();
            expect('=>');

            returnType = parseTypeAnnotation(true);
        } else {
            if (!matchKeyword('void')) {
                throwUnexpected(lookahead);
            } else {
                return markerApply(marker, parseVoidTypeAnnotation());
            }
        }

        return markerApply(marker, delegate.createTypeAnnotation(
            typeIdentifier,
            parametricType,
            params,
            returnType,
            nullable
        ));
    }

    function parseVariableIdentifier() {
        var marker = markerCreate(),
            token = lex();

        if (token.type !== Token.Identifier) {
            throwUnexpected(token);
        }

        return markerApply(marker, delegate.createIdentifier(token.value));
    }

    function parseTypeAnnotatableIdentifier(requireTypeAnnotation, canBeOptionalParam) {
        var marker = markerCreate(),
            ident = parseVariableIdentifier(),
            isOptionalParam = false;

        if (canBeOptionalParam && match('?')) {
            expect('?');
            isOptionalParam = true;
        }

        if (requireTypeAnnotation || match(':')) {
            ident = markerApply(marker, delegate.createTypeAnnotatedIdentifier(
                ident,
                parseTypeAnnotation()
            ));
        }

        if (isOptionalParam) {
            ident = markerApply(marker, delegate.createOptionalParameter(ident));
        }

        return ident;
    }

    function parseVariableDeclaration(kind) {
        var id,
            marker = markerCreate(),
            init = null;
        if (match('{')) {
            id = parseObjectInitialiser();
            reinterpretAsAssignmentBindingPattern(id);
        } else if (match('[')) {
            id = parseArrayInitialiser();
            reinterpretAsAssignmentBindingPattern(id);
        } else {
            id = state.allowKeyword ? parseNonComputedProperty() : parseTypeAnnotatableIdentifier();
            // 12.2.1
            if (strict && isRestrictedWord(id.name)) {
                throwErrorTolerant({}, Messages.StrictVarName);
            }
        }

        if (kind === 'const') {
            if (!match('=')) {
                throwError({}, Messages.NoUnintializedConst);
            }
            expect('=');
            init = parseAssignmentExpression();
        } else if (match('=')) {
            lex();
            init = parseAssignmentExpression();
        }

        return markerApply(marker, delegate.createVariableDeclarator(id, init));
    }

    function parseVariableDeclarationList(kind) {
        var list = [];

        do {
            list.push(parseVariableDeclaration(kind));
            if (!match(',')) {
                break;
            }
            lex();
        } while (index < length);

        return list;
    }

    function parseVariableStatement() {
        var declarations, marker = markerCreate();

        expectKeyword('var');

        declarations = parseVariableDeclarationList();

        consumeSemicolon();

        return markerApply(marker, delegate.createVariableDeclaration(declarations, 'var'));
    }

    // kind may be `const` or `let`
    // Both are experimental and not in the specification yet.
    // see http://wiki.ecmascript.org/doku.php?id=harmony:const
    // and http://wiki.ecmascript.org/doku.php?id=harmony:let
    function parseConstLetDeclaration(kind) {
        var declarations, marker = markerCreate();

        expectKeyword(kind);

        declarations = parseVariableDeclarationList(kind);

        consumeSemicolon();

        return markerApply(marker, delegate.createVariableDeclaration(declarations, kind));
    }

    // people.mozilla.org/~jorendorff/es6-draft.html

    function parseModuleSpecifier() {
        var marker = markerCreate(),
            specifier;

        if (lookahead.type !== Token.StringLiteral) {
            throwError({}, Messages.InvalidModuleSpecifier);
        }
        specifier = delegate.createModuleSpecifier(lookahead);
        lex();
        return markerApply(marker, specifier);
    }

    function parseExportBatchSpecifier() {
        var marker = markerCreate();
        expect('*');
        return markerApply(marker, delegate.createExportBatchSpecifier());
    }

    function parseExportSpecifier() {
        var id, name = null, marker = markerCreate(), from;
        if (matchKeyword('default')) {
            lex();
            id = markerApply(marker, delegate.createIdentifier('default'));
            // export {default} from "something";
        } else {
            id = parseVariableIdentifier();
        }
        if (matchContextualKeyword('as')) {
            lex();
            name = parseNonComputedProperty();
        }

        return markerApply(marker, delegate.createExportSpecifier(id, name));
    }

    function parseExportDeclaration() {
        var backtrackToken, id, previousAllowKeyword, declaration = null,
            isExportFromIdentifier,
            src = null, specifiers = [],
            marker = markerCreate();

        expectKeyword('export');

        if (matchKeyword('default')) {
            // covers:
            // export default ...
            lex();
            if (matchKeyword('function') || matchKeyword('class')) {
                backtrackToken = lookahead;
                lex();
                if (isIdentifierName(lookahead)) {
                    // covers:
                    // export default function foo () {}
                    // export default class foo {}
                    id = parseNonComputedProperty();
                    rewind(backtrackToken);
                    return markerApply(marker, delegate.createExportDeclaration(true, parseSourceElement(), [id], null));
                }
                // covers:
                // export default function () {}
                // export default class {}
                rewind(backtrackToken);
                switch (lookahead.value) {
                case 'class':
                    return markerApply(marker, delegate.createExportDeclaration(true, parseClassExpression(), [], null));
                case 'function':
                    return markerApply(marker, delegate.createExportDeclaration(true, parseFunctionExpression(), [], null));
                }
            }

            if (matchContextualKeyword('from')) {
                throwError({}, Messages.UnexpectedToken, lookahead.value);
            }

            // covers:
            // export default {};
            // export default [];
            if (match('{')) {
                declaration = parseObjectInitialiser();
            } else if (match('[')) {
                declaration = parseArrayInitialiser();
            } else {
                declaration = parseAssignmentExpression();
            }
            consumeSemicolon();
            return markerApply(marker, delegate.createExportDeclaration(true, declaration, [], null));
        }

        // non-default export
        if (lookahead.type === Token.Keyword) {
            // covers:
            // export var f = 1;
            switch (lookahead.value) {
            case 'let':
            case 'const':
            case 'var':
            case 'class':
            case 'function':
                return markerApply(marker, delegate.createExportDeclaration(false, parseSourceElement(), specifiers, null));
            }
        }

        if (match('*')) {
            // covers:
            // export * from "foo";
            specifiers.push(parseExportBatchSpecifier());

            if (!matchContextualKeyword('from')) {
                throwError({}, lookahead.value ?
                        Messages.UnexpectedToken : Messages.MissingFromClause, lookahead.value);
            }
            lex();
            src = parseModuleSpecifier();
            consumeSemicolon();

            return markerApply(marker, delegate.createExportDeclaration(false, null, specifiers, src));
        }

        expect('{');
        do {
            isExportFromIdentifier = isExportFromIdentifier || matchKeyword('default');
            specifiers.push(parseExportSpecifier());
        } while (match(',') && lex());
        expect('}');

        if (matchContextualKeyword('from')) {
            // covering:
            // export {default} from "foo";
            // export {foo} from "foo";
            lex();
            src = parseModuleSpecifier();
            consumeSemicolon();
        } else if (isExportFromIdentifier) {
            // covering:
            // export {default}; // missing fromClause
            throwError({}, lookahead.value ?
                    Messages.UnexpectedToken : Messages.MissingFromClause, lookahead.value);
        } else {
            // cover
            // export {foo};
            consumeSemicolon();
        }
        return markerApply(marker, delegate.createExportDeclaration(false, declaration, specifiers, src));
    }


    function parseImportSpecifier() {
        // import {<foo as bar>} ...;
        var id, name = null, marker = markerCreate();

        id = parseNonComputedProperty();
        if (matchContextualKeyword('as')) {
            lex();
            name = parseVariableIdentifier();
        }

        return markerApply(marker, delegate.createImportSpecifier(id, name));
    }

    function parseNamedImports() {
        var specifiers = [];
        // {foo, bar as bas}
        expect('{');
        do {
            specifiers.push(parseImportSpecifier());
        } while (match(',') && lex());
        expect('}');
        return specifiers;
    }

    function parseImportDefaultSpecifier() {
        // import <foo> ...;
        var id, marker = markerCreate();

        id = parseNonComputedProperty();

        return markerApply(marker, delegate.createImportDefaultSpecifier(id));
    }

    function parseImportNamespaceSpecifier() {
        // import <* as foo> ...;
        var id, marker = markerCreate();

        expect('*');
        if (!matchContextualKeyword('as')) {
            throwError({}, Messages.NoAsAfterImportNamespace);
        }
        lex();
        id = parseNonComputedProperty();

        return markerApply(marker, delegate.createImportNamespaceSpecifier(id));
    }

    function parseImportDeclaration() {
        var specifiers, src, marker = markerCreate();

        expectKeyword('import');
        specifiers = [];

        if (lookahead.type === Token.StringLiteral) {
            // covers:
            // import "foo";
            src = parseModuleSpecifier();
            consumeSemicolon();
            return markerApply(marker, delegate.createImportDeclaration(specifiers, src));
        }

        if (!matchKeyword('default') && isIdentifierName(lookahead)) {
            // covers:
            // import foo
            // import foo, ...
            specifiers.push(parseImportDefaultSpecifier());
            if (match(',')) {
                lex();
            }
        }
        if (match('*')) {
            // covers:
            // import foo, * as foo
            // import * as foo
            specifiers.push(parseImportNamespaceSpecifier());
        } else if (match('{')) {
            // covers:
            // import foo, {bar}
            // import {bar}
            specifiers = specifiers.concat(parseNamedImports());
        }

        if (!matchContextualKeyword('from')) {
            throwError({}, lookahead.value ?
                    Messages.UnexpectedToken : Messages.MissingFromClause, lookahead.value);
        }
        lex();
        src = parseModuleSpecifier();
        consumeSemicolon();

        return markerApply(marker, delegate.createImportDeclaration(specifiers, src));
    }

    // 12.3 Empty Statement

    function parseEmptyStatement() {
        var marker = markerCreate();
        expect(';');
        return markerApply(marker, delegate.createEmptyStatement());
    }

    // 12.4 Expression Statement

    function parseExpressionStatement() {
        var marker = markerCreate(), expr = parseExpression();
        consumeSemicolon();
        return markerApply(marker, delegate.createExpressionStatement(expr));
    }

    // 12.5 If statement

    function parseIfStatement() {
        var test, consequent, alternate, marker = markerCreate();

        expectKeyword('if');

        expect('(');

        test = parseExpression();

        expect(')');

        consequent = parseStatement();

        if (matchKeyword('else')) {
            lex();
            alternate = parseStatement();
        } else {
            alternate = null;
        }

        return markerApply(marker, delegate.createIfStatement(test, consequent, alternate));
    }

    // 12.6 Iteration Statements

    function parseDoWhileStatement() {
        var body, test, oldInIteration, marker = markerCreate();

        expectKeyword('do');

        oldInIteration = state.inIteration;
        state.inIteration = true;

        body = parseStatement();

        state.inIteration = oldInIteration;

        expectKeyword('while');

        expect('(');

        test = parseExpression();

        expect(')');

        if (match(';')) {
            lex();
        }

        return markerApply(marker, delegate.createDoWhileStatement(body, test));
    }

    function parseWhileStatement() {
        var test, body, oldInIteration, marker = markerCreate();

        expectKeyword('while');

        expect('(');

        test = parseExpression();

        expect(')');

        oldInIteration = state.inIteration;
        state.inIteration = true;

        body = parseStatement();

        state.inIteration = oldInIteration;

        return markerApply(marker, delegate.createWhileStatement(test, body));
    }

    function parseForVariableDeclaration() {
        var marker = markerCreate(),
            token = lex(),
            declarations = parseVariableDeclarationList();

        return markerApply(marker, delegate.createVariableDeclaration(declarations, token.value));
    }

    function parseForStatement(opts) {
        var init, test, update, left, right, body, operator, oldInIteration,
            marker = markerCreate();
        init = test = update = null;
        expectKeyword('for');

        // http://wiki.ecmascript.org/doku.php?id=proposals:iterators_and_generators&s=each
        if (matchContextualKeyword('each')) {
            throwError({}, Messages.EachNotAllowed);
        }

        expect('(');

        if (match(';')) {
            lex();
        } else {
            if (matchKeyword('var') || matchKeyword('let') || matchKeyword('const')) {
                state.allowIn = false;
                init = parseForVariableDeclaration();
                state.allowIn = true;

                if (init.declarations.length === 1) {
                    if (matchKeyword('in') || matchContextualKeyword('of')) {
                        operator = lookahead;
                        if (!((operator.value === 'in' || init.kind !== 'var') && init.declarations[0].init)) {
                            lex();
                            left = init;
                            right = parseExpression();
                            init = null;
                        }
                    }
                }
            } else {
                state.allowIn = false;
                init = parseExpression();
                state.allowIn = true;

                if (matchContextualKeyword('of')) {
                    operator = lex();
                    left = init;
                    right = parseExpression();
                    init = null;
                } else if (matchKeyword('in')) {
                    // LeftHandSideExpression
                    if (!isAssignableLeftHandSide(init)) {
                        throwError({}, Messages.InvalidLHSInForIn);
                    }
                    operator = lex();
                    left = init;
                    right = parseExpression();
                    init = null;
                }
            }

            if (typeof left === 'undefined') {
                expect(';');
            }
        }

        if (typeof left === 'undefined') {

            if (!match(';')) {
                test = parseExpression();
            }
            expect(';');

            if (!match(')')) {
                update = parseExpression();
            }
        }

        expect(')');

        oldInIteration = state.inIteration;
        state.inIteration = true;

        if (!(opts !== undefined && opts.ignoreBody)) {
            body = parseStatement();
        }

        state.inIteration = oldInIteration;

        if (typeof left === 'undefined') {
            return markerApply(marker, delegate.createForStatement(init, test, update, body));
        }

        if (operator.value === 'in') {
            return markerApply(marker, delegate.createForInStatement(left, right, body));
        }
        return markerApply(marker, delegate.createForOfStatement(left, right, body));
    }

    // 12.7 The continue statement

    function parseContinueStatement() {
        var label = null, key, marker = markerCreate();

        expectKeyword('continue');

        // Optimize the most common form: 'continue;'.
        if (source.charCodeAt(index) === 59) {
            lex();

            if (!state.inIteration) {
                throwError({}, Messages.IllegalContinue);
            }

            return markerApply(marker, delegate.createContinueStatement(null));
        }

        if (peekLineTerminator()) {
            if (!state.inIteration) {
                throwError({}, Messages.IllegalContinue);
            }

            return markerApply(marker, delegate.createContinueStatement(null));
        }

        if (lookahead.type === Token.Identifier) {
            label = parseVariableIdentifier();

            key = '$' + label.name;
            if (!Object.prototype.hasOwnProperty.call(state.labelSet, key)) {
                throwError({}, Messages.UnknownLabel, label.name);
            }
        }

        consumeSemicolon();

        if (label === null && !state.inIteration) {
            throwError({}, Messages.IllegalContinue);
        }

        return markerApply(marker, delegate.createContinueStatement(label));
    }

    // 12.8 The break statement

    function parseBreakStatement() {
        var label = null, key, marker = markerCreate();

        expectKeyword('break');

        // Catch the very common case first: immediately a semicolon (char #59).
        if (source.charCodeAt(index) === 59) {
            lex();

            if (!(state.inIteration || state.inSwitch)) {
                throwError({}, Messages.IllegalBreak);
            }

            return markerApply(marker, delegate.createBreakStatement(null));
        }

        if (peekLineTerminator()) {
            if (!(state.inIteration || state.inSwitch)) {
                throwError({}, Messages.IllegalBreak);
            }

            return markerApply(marker, delegate.createBreakStatement(null));
        }

        if (lookahead.type === Token.Identifier) {
            label = parseVariableIdentifier();

            key = '$' + label.name;
            if (!Object.prototype.hasOwnProperty.call(state.labelSet, key)) {
                throwError({}, Messages.UnknownLabel, label.name);
            }
        }

        consumeSemicolon();

        if (label === null && !(state.inIteration || state.inSwitch)) {
            throwError({}, Messages.IllegalBreak);
        }

        return markerApply(marker, delegate.createBreakStatement(label));
    }

    // 12.9 The return statement

    function parseReturnStatement() {
        var argument = null, marker = markerCreate();

        expectKeyword('return');

        if (!state.inFunctionBody) {
            throwErrorTolerant({}, Messages.IllegalReturn);
        }

        // 'return' followed by a space and an identifier is very common.
        if (source.charCodeAt(index) === 32) {
            if (isIdentifierStart(source.charCodeAt(index + 1))) {
                argument = parseExpression();
                consumeSemicolon();
                return markerApply(marker, delegate.createReturnStatement(argument));
            }
        }

        if (peekLineTerminator()) {
            return markerApply(marker, delegate.createReturnStatement(null));
        }

        if (!match(';')) {
            if (!match('}') && lookahead.type !== Token.EOF) {
                argument = parseExpression();
            }
        }

        consumeSemicolon();

        return markerApply(marker, delegate.createReturnStatement(argument));
    }

    // 12.10 The with statement

    function parseWithStatement() {
        var object, body, marker = markerCreate();

        if (strict) {
            throwErrorTolerant({}, Messages.StrictModeWith);
        }

        expectKeyword('with');

        expect('(');

        object = parseExpression();

        expect(')');

        body = parseStatement();

        return markerApply(marker, delegate.createWithStatement(object, body));
    }

    // 12.10 The swith statement

    function parseSwitchCase() {
        var test,
            consequent = [],
            sourceElement,
            marker = markerCreate();

        if (matchKeyword('default')) {
            lex();
            test = null;
        } else {
            expectKeyword('case');
            test = parseExpression();
        }
        expect(':');

        while (index < length) {
            if (match('}') || matchKeyword('default') || matchKeyword('case')) {
                break;
            }
            sourceElement = parseSourceElement();
            if (typeof sourceElement === 'undefined') {
                break;
            }
            consequent.push(sourceElement);
        }

        return markerApply(marker, delegate.createSwitchCase(test, consequent));
    }

    function parseSwitchStatement() {
        var discriminant, cases, clause, oldInSwitch, defaultFound, marker = markerCreate();

        expectKeyword('switch');

        expect('(');

        discriminant = parseExpression();

        expect(')');

        expect('{');

        cases = [];

        if (match('}')) {
            lex();
            return markerApply(marker, delegate.createSwitchStatement(discriminant, cases));
        }

        oldInSwitch = state.inSwitch;
        state.inSwitch = true;
        defaultFound = false;

        while (index < length) {
            if (match('}')) {
                break;
            }
            clause = parseSwitchCase();
            if (clause.test === null) {
                if (defaultFound) {
                    throwError({}, Messages.MultipleDefaultsInSwitch);
                }
                defaultFound = true;
            }
            cases.push(clause);
        }

        state.inSwitch = oldInSwitch;

        expect('}');

        return markerApply(marker, delegate.createSwitchStatement(discriminant, cases));
    }

    // 12.13 The throw statement

    function parseThrowStatement() {
        var argument, marker = markerCreate();

        expectKeyword('throw');

        if (peekLineTerminator()) {
            throwError({}, Messages.NewlineAfterThrow);
        }

        argument = parseExpression();

        consumeSemicolon();

        return markerApply(marker, delegate.createThrowStatement(argument));
    }

    // 12.14 The try statement

    function parseCatchClause() {
        var param, body, marker = markerCreate();

        expectKeyword('catch');

        expect('(');
        if (match(')')) {
            throwUnexpected(lookahead);
        }

        param = parseExpression();
        // 12.14.1
        if (strict && param.type === Syntax.Identifier && isRestrictedWord(param.name)) {
            throwErrorTolerant({}, Messages.StrictCatchVariable);
        }

        expect(')');
        body = parseBlock();
        return markerApply(marker, delegate.createCatchClause(param, body));
    }

    function parseTryStatement() {
        var block, handlers = [], finalizer = null, marker = markerCreate();

        expectKeyword('try');

        block = parseBlock();

        if (matchKeyword('catch')) {
            handlers.push(parseCatchClause());
        }

        if (matchKeyword('finally')) {
            lex();
            finalizer = parseBlock();
        }

        if (handlers.length === 0 && !finalizer) {
            throwError({}, Messages.NoCatchOrFinally);
        }

        return markerApply(marker, delegate.createTryStatement(block, [], handlers, finalizer));
    }

    // 12.15 The debugger statement

    function parseDebuggerStatement() {
        var marker = markerCreate();
        expectKeyword('debugger');

        consumeSemicolon();

        return markerApply(marker, delegate.createDebuggerStatement());
    }

    // 12 Statements

    function parseStatement() {
        var type = lookahead.type,
            marker,
            expr,
            labeledBody,
            key;

        if (type === Token.EOF) {
            throwUnexpected(lookahead);
        }

        if (type === Token.Punctuator) {
            switch (lookahead.value) {
            case ';':
                return parseEmptyStatement();
            case '{':
                return parseBlock();
            case '(':
                return parseExpressionStatement();
            default:
                break;
            }
        }

        if (type === Token.Keyword) {
            switch (lookahead.value) {
            case 'break':
                return parseBreakStatement();
            case 'continue':
                return parseContinueStatement();
            case 'debugger':
                return parseDebuggerStatement();
            case 'do':
                return parseDoWhileStatement();
            case 'for':
                return parseForStatement();
            case 'function':
                return parseFunctionDeclaration();
            case 'class':
                return parseClassDeclaration();
            case 'if':
                return parseIfStatement();
            case 'return':
                return parseReturnStatement();
            case 'switch':
                return parseSwitchStatement();
            case 'throw':
                return parseThrowStatement();
            case 'try':
                return parseTryStatement();
            case 'var':
                return parseVariableStatement();
            case 'while':
                return parseWhileStatement();
            case 'with':
                return parseWithStatement();
            default:
                break;
            }
        }

        if (matchAsyncFuncExprOrDecl()) {
            return parseFunctionDeclaration();
        }

        marker = markerCreate();
        expr = parseExpression();

        // 12.12 Labelled Statements
        if ((expr.type === Syntax.Identifier) && match(':')) {
            lex();

            key = '$' + expr.name;
            if (Object.prototype.hasOwnProperty.call(state.labelSet, key)) {
                throwError({}, Messages.Redeclaration, 'Label', expr.name);
            }

            state.labelSet[key] = true;
            labeledBody = parseStatement();
            delete state.labelSet[key];
            return markerApply(marker, delegate.createLabeledStatement(expr, labeledBody));
        }

        consumeSemicolon();

        return markerApply(marker, delegate.createExpressionStatement(expr));
    }

    // 13 Function Definition

    function parseConciseBody() {
        if (match('{')) {
            return parseFunctionSourceElements();
        }
        return parseAssignmentExpression();
    }

    function parseFunctionSourceElements() {
        var sourceElement, sourceElements = [], token, directive, firstRestricted,
            oldLabelSet, oldInIteration, oldInSwitch, oldInFunctionBody, oldParenthesizedCount,
            marker = markerCreate();

        expect('{');

        while (index < length) {
            if (lookahead.type !== Token.StringLiteral) {
                break;
            }
            token = lookahead;

            sourceElement = parseSourceElement();
            sourceElements.push(sourceElement);
            if (sourceElement.expression.type !== Syntax.Literal) {
                // this is not directive
                break;
            }
            directive = source.slice(token.range[0] + 1, token.range[1] - 1);
            if (directive === 'use strict') {
                strict = true;
                if (firstRestricted) {
                    throwErrorTolerant(firstRestricted, Messages.StrictOctalLiteral);
                }
            } else {
                if (!firstRestricted && token.octal) {
                    firstRestricted = token;
                }
            }
        }

        oldLabelSet = state.labelSet;
        oldInIteration = state.inIteration;
        oldInSwitch = state.inSwitch;
        oldInFunctionBody = state.inFunctionBody;
        oldParenthesizedCount = state.parenthesizedCount;

        state.labelSet = {};
        state.inIteration = false;
        state.inSwitch = false;
        state.inFunctionBody = true;
        state.parenthesizedCount = 0;

        while (index < length) {
            if (match('}')) {
                break;
            }
            sourceElement = parseSourceElement();
            if (typeof sourceElement === 'undefined') {
                break;
            }
            sourceElements.push(sourceElement);
        }

        expect('}');

        state.labelSet = oldLabelSet;
        state.inIteration = oldInIteration;
        state.inSwitch = oldInSwitch;
        state.inFunctionBody = oldInFunctionBody;
        state.parenthesizedCount = oldParenthesizedCount;

        return markerApply(marker, delegate.createBlockStatement(sourceElements));
    }

    function validateParam(options, param, name) {
        var key = '$' + name;
        if (strict) {
            if (isRestrictedWord(name)) {
                options.stricted = param;
                options.message = Messages.StrictParamName;
            }
            if (Object.prototype.hasOwnProperty.call(options.paramSet, key)) {
                options.stricted = param;
                options.message = Messages.StrictParamDupe;
            }
        } else if (!options.firstRestricted) {
            if (isRestrictedWord(name)) {
                options.firstRestricted = param;
                options.message = Messages.StrictParamName;
            } else if (isStrictModeReservedWord(name)) {
                options.firstRestricted = param;
                options.message = Messages.StrictReservedWord;
            } else if (Object.prototype.hasOwnProperty.call(options.paramSet, key)) {
                options.firstRestricted = param;
                options.message = Messages.StrictParamDupe;
            }
        }
        options.paramSet[key] = true;
    }

    function parseParam(options) {
        var token, rest, param, def;

        token = lookahead;
        if (token.value === '...') {
            token = lex();
            rest = true;
        }

        if (match('[')) {
            param = parseArrayInitialiser();
            reinterpretAsDestructuredParameter(options, param);
        } else if (match('{')) {
            if (rest) {
                throwError({}, Messages.ObjectPatternAsRestParameter);
            }
            param = parseObjectInitialiser();
            reinterpretAsDestructuredParameter(options, param);
        } else {
            // Typing rest params is awkward, so punting on that for now
            param =
                rest
                ? parseVariableIdentifier()
                : parseTypeAnnotatableIdentifier(
                    false, /* requireTypeAnnotation */
                    true /* canBeOptionalParam */
                );

            validateParam(options, token, token.value);
        }

        if (match('=')) {
            if (rest) {
                throwErrorTolerant(lookahead, Messages.DefaultRestParameter);
            }
            lex();
            def = parseAssignmentExpression();
            ++options.defaultCount;
        }

        if (rest) {
            if (!match(')')) {
                throwError({}, Messages.ParameterAfterRestParameter);
            }
            options.rest = param;
            return false;
        }

        options.params.push(param);
        options.defaults.push(def);
        return !match(')');
    }

    function parseParams(firstRestricted) {
        var options, marker = markerCreate();

        options = {
            params: [],
            defaultCount: 0,
            defaults: [],
            rest: null,
            firstRestricted: firstRestricted
        };

        expect('(');

        if (!match(')')) {
            options.paramSet = {};
            while (index < length) {
                if (!parseParam(options)) {
                    break;
                }
                expect(',');
            }
        }

        expect(')');

        if (options.defaultCount === 0) {
            options.defaults = [];
        }

        if (match(':')) {
            options.returnType = parseTypeAnnotation();
        }

        return markerApply(marker, options);
    }

    function parseFunctionDeclaration() {
        var id, body, token, tmp, firstRestricted, message, generator, isAsync,
            previousStrict, previousYieldAllowed, previousAwaitAllowed,
            marker = markerCreate(), parametricType;

        isAsync = false;
        if (matchAsync()) {
            lex();
            isAsync = true;
        }

        expectKeyword('function');

        generator = false;
        if (match('*')) {
            lex();
            generator = true;
        }

        token = lookahead;

        id = parseVariableIdentifier();

        if (match('<')) {
            parametricType = parseParametricTypeAnnotation();
        }

        if (strict) {
            if (isRestrictedWord(token.value)) {
                throwErrorTolerant(token, Messages.StrictFunctionName);
            }
        } else {
            if (isRestrictedWord(token.value)) {
                firstRestricted = token;
                message = Messages.StrictFunctionName;
            } else if (isStrictModeReservedWord(token.value)) {
                firstRestricted = token;
                message = Messages.StrictReservedWord;
            }
        }

        tmp = parseParams(firstRestricted);
        firstRestricted = tmp.firstRestricted;
        if (tmp.message) {
            message = tmp.message;
        }

        previousStrict = strict;
        previousYieldAllowed = state.yieldAllowed;
        state.yieldAllowed = generator;
        previousAwaitAllowed = state.awaitAllowed;
        state.awaitAllowed = isAsync;

        body = parseFunctionSourceElements();

        if (strict && firstRestricted) {
            throwError(firstRestricted, message);
        }
        if (strict && tmp.stricted) {
            throwErrorTolerant(tmp.stricted, message);
        }
        strict = previousStrict;
        state.yieldAllowed = previousYieldAllowed;
        state.awaitAllowed = previousAwaitAllowed;

        return markerApply(
            marker,
            delegate.createFunctionDeclaration(
                id,
                tmp.params,
                tmp.defaults,
                body,
                tmp.rest,
                generator,
                false,
                isAsync,
                tmp.returnType,
                parametricType
            )
        );
    }

    function parseFunctionExpression() {
        var token, id = null, firstRestricted, message, tmp, body, generator, isAsync,
            previousStrict, previousYieldAllowed, previousAwaitAllowed,
            marker = markerCreate(), parametricType;

        isAsync = false;
        if (matchAsync()) {
            lex();
            isAsync = true;
        }

        expectKeyword('function');

        generator = false;

        if (match('*')) {
            lex();
            generator = true;
        }

        if (!match('(')) {
            if (!match('<')) {
                token = lookahead;
                id = parseVariableIdentifier();

                if (strict) {
                    if (isRestrictedWord(token.value)) {
                        throwErrorTolerant(token, Messages.StrictFunctionName);
                    }
                } else {
                    if (isRestrictedWord(token.value)) {
                        firstRestricted = token;
                        message = Messages.StrictFunctionName;
                    } else if (isStrictModeReservedWord(token.value)) {
                        firstRestricted = token;
                        message = Messages.StrictReservedWord;
                    }
                }
            }

            if (match('<')) {
                parametricType = parseParametricTypeAnnotation();
            }
        }

        tmp = parseParams(firstRestricted);
        firstRestricted = tmp.firstRestricted;
        if (tmp.message) {
            message = tmp.message;
        }

        previousStrict = strict;
        previousYieldAllowed = state.yieldAllowed;
        state.yieldAllowed = generator;
        previousAwaitAllowed = state.awaitAllowed;
        state.awaitAllowed = isAsync;

        body = parseFunctionSourceElements();

        if (strict && firstRestricted) {
            throwError(firstRestricted, message);
        }
        if (strict && tmp.stricted) {
            throwErrorTolerant(tmp.stricted, message);
        }
        strict = previousStrict;
        state.yieldAllowed = previousYieldAllowed;
        state.awaitAllowed = previousAwaitAllowed;

        return markerApply(
            marker,
            delegate.createFunctionExpression(
                id,
                tmp.params,
                tmp.defaults,
                body,
                tmp.rest,
                generator,
                false,
                isAsync,
                tmp.returnType,
                parametricType
            )
        );
    }

    function parseYieldExpression() {
        var delegateFlag, expr, marker = markerCreate();

        expectKeyword('yield', !strict);

        delegateFlag = false;
        if (match('*')) {
            lex();
            delegateFlag = true;
        }

        expr = parseAssignmentExpression();

        return markerApply(marker, delegate.createYieldExpression(expr, delegateFlag));
    }

    function parseAwaitExpression() {
        var expr, marker = markerCreate();
        expectContextualKeyword('await');
        expr = parseAssignmentExpression();
        return markerApply(marker, delegate.createAwaitExpression(expr));
    }

    // 14 Classes

    function parseMethodDefinition(existingPropNames) {
        var token, key, param, propType, isValidDuplicateProp = false,
            isAsync, marker = markerCreate(), token2, parametricType,
            parametricTypeMarker, annotationMarker;

        if (lookahead.value === 'static') {
            propType = ClassPropertyType.static;
            lex();
        } else {
            propType = ClassPropertyType.prototype;
        }

        if (match('*')) {
            lex();
            return markerApply(marker, delegate.createMethodDefinition(
                propType,
                '',
                parseObjectPropertyKey(),
                parsePropertyMethodFunction({ generator: true })
            ));
        }

        token = lookahead;
        //parametricTypeMarker = markerCreate();
        key = parseObjectPropertyKey();

        if (token.value === 'get' && !match('(')) {
            key = parseObjectPropertyKey();

            // It is a syntax error if any other properties have a name
            // duplicating this one unless they are a setter
            if (existingPropNames[propType].hasOwnProperty(key.name)) {
                isValidDuplicateProp =
                    // There isn't already a getter for this prop
                    existingPropNames[propType][key.name].get === undefined
                    // There isn't already a data prop by this name
                    && existingPropNames[propType][key.name].data === undefined
                    // The only existing prop by this name is a setter
                    && existingPropNames[propType][key.name].set !== undefined;
                if (!isValidDuplicateProp) {
                    throwError(key, Messages.IllegalDuplicateClassProperty);
                }
            } else {
                existingPropNames[propType][key.name] = {};
            }
            existingPropNames[propType][key.name].get = true;

            expect('(');
            expect(')');
            return markerApply(marker, delegate.createMethodDefinition(
                propType,
                'get',
                key,
                parsePropertyFunction({ generator: false })
            ));
        }
        if (token.value === 'set' && !match('(')) {
            key = parseObjectPropertyKey();

            // It is a syntax error if any other properties have a name
            // duplicating this one unless they are a getter
            if (existingPropNames[propType].hasOwnProperty(key.name)) {
                isValidDuplicateProp =
                    // There isn't already a setter for this prop
                    existingPropNames[propType][key.name].set === undefined
                    // There isn't already a data prop by this name
                    && existingPropNames[propType][key.name].data === undefined
                    // The only existing prop by this name is a getter
                    && existingPropNames[propType][key.name].get !== undefined;
                if (!isValidDuplicateProp) {
                    throwError(key, Messages.IllegalDuplicateClassProperty);
                }
            } else {
                existingPropNames[propType][key.name] = {};
            }
            existingPropNames[propType][key.name].set = true;

            expect('(');
            token = lookahead;
            param = [ parseTypeAnnotatableIdentifier() ];
            expect(')');
            return markerApply(marker, delegate.createMethodDefinition(
                propType,
                'set',
                key,
                parsePropertyFunction({ params: param, generator: false, name: token })
            ));
        }

        if (match('<')) {
            parametricType = parseParametricTypeAnnotation();
        }

        isAsync = token.value === 'async' && !match('(');
        if (isAsync) {
            key = parseObjectPropertyKey();
        }

        // It is a syntax error if any other properties have the same name as a
        // non-getter, non-setter method
        if (existingPropNames[propType].hasOwnProperty(key.name)) {
            throwError(key, Messages.IllegalDuplicateClassProperty);
        } else {
            existingPropNames[propType][key.name] = {};
        }
        existingPropNames[propType][key.name].data = true;

        return markerApply(marker, delegate.createMethodDefinition(
            propType,
            '',
            key,
            parsePropertyMethodFunction({
                generator: false,
                async: isAsync,
                parametricType: parametricType
            })
        ));
    }

    function parseClassProperty(existingPropNames) {
        var marker = markerCreate(), propertyIdentifier;

        propertyIdentifier = parseTypeAnnotatableIdentifier();
        expect(';');

        return markerApply(marker, delegate.createClassProperty(
            propertyIdentifier
        ));
    }

    function parseClassElement(existingProps) {
        if (match(';')) {
            lex();
            return;
        }

        var doubleLookahead = lookahead2();
        if (doubleLookahead.type === Token.Punctuator) {
            if (doubleLookahead.value === ':') {
                return parseClassProperty(existingProps);
            }
        }

        return parseMethodDefinition(existingProps);
    }

    function parseClassBody() {
        var classElement, classElements = [], existingProps = {}, marker = markerCreate();

        existingProps[ClassPropertyType.static] = {};
        existingProps[ClassPropertyType.prototype] = {};

        expect('{');

        while (index < length) {
            if (match('}')) {
                break;
            }
            classElement = parseClassElement(existingProps);

            if (typeof classElement !== 'undefined') {
                classElements.push(classElement);
            }
        }

        expect('}');

        return markerApply(marker, delegate.createClassBody(classElements));
    }

    function parseClassExpression() {
        var id, previousYieldAllowed, superClass = null, marker = markerCreate(),
            parametricType;

        expectKeyword('class');

        if (!matchKeyword('extends') && !match('{')) {
            id = parseVariableIdentifier();
        }

        if (match('<')) {
            parametricType = parseParametricTypeAnnotation();
        }

        if (matchKeyword('extends')) {
            expectKeyword('extends');
            previousYieldAllowed = state.yieldAllowed;
            state.yieldAllowed = false;
            superClass = parseAssignmentExpression();
            state.yieldAllowed = previousYieldAllowed;
        }

        return markerApply(marker, delegate.createClassExpression(id, superClass, parseClassBody(), parametricType));
    }

    function parseClassDeclaration() {
        var id, previousYieldAllowed, superClass = null, marker = markerCreate(),
            parametricType, superParametricType;

        expectKeyword('class');

        id = parseVariableIdentifier();

        if (match('<')) {
            parametricType = parseParametricTypeAnnotation();
        }

        if (matchKeyword('extends')) {
            expectKeyword('extends');
            previousYieldAllowed = state.yieldAllowed;
            state.yieldAllowed = false;
            superClass = parseAssignmentExpression();
            state.yieldAllowed = previousYieldAllowed;
        }

        return markerApply(marker, delegate.createClassDeclaration(id, superClass, parseClassBody(), parametricType, superParametricType));
    }

    // 15 Program

    function parseSourceElement() {
        if (lookahead.type === Token.Keyword) {
            switch (lookahead.value) {
            case 'const':
            case 'let':
                return parseConstLetDeclaration(lookahead.value);
            case 'function':
                return parseFunctionDeclaration();
            default:
                return parseStatement();
            }
        }

        if (lookahead.type !== Token.EOF) {
            return parseStatement();
        }
    }

    function parseProgramElement() {
        if (lookahead.type === Token.Keyword) {
            switch (lookahead.value) {
            case 'export':
                return parseExportDeclaration();
            case 'import':
                return parseImportDeclaration();
            }
        }

        return parseSourceElement();
    }

    function parseProgramElements() {
        var sourceElement, sourceElements = [], token, directive, firstRestricted;

        while (index < length) {
            token = lookahead;
            if (token.type !== Token.StringLiteral) {
                break;
            }

            sourceElement = parseProgramElement();
            sourceElements.push(sourceElement);
            if (sourceElement.expression.type !== Syntax.Literal) {
                // this is not directive
                break;
            }
            directive = source.slice(token.range[0] + 1, token.range[1] - 1);
            if (directive === 'use strict') {
                strict = true;
                if (firstRestricted) {
                    throwErrorTolerant(firstRestricted, Messages.StrictOctalLiteral);
                }
            } else {
                if (!firstRestricted && token.octal) {
                    firstRestricted = token;
                }
            }
        }

        while (index < length) {
            sourceElement = parseProgramElement();
            if (typeof sourceElement === 'undefined') {
                break;
            }
            sourceElements.push(sourceElement);
        }
        return sourceElements;
    }

    function parseProgram() {
        var body, marker = markerCreate();
        strict = false;
        peek();
        body = parseProgramElements();
        return markerApply(marker, delegate.createProgram(body));
    }

    // The following functions are needed only when the option to preserve
    // the comments is active.

    function addComment(type, value, start, end, loc) {
        var comment;

        assert(typeof start === 'number', 'Comment must have valid position');

        // Because the way the actual token is scanned, often the comments
        // (if any) are skipped twice during the lexical analysis.
        // Thus, we need to skip adding a comment if the comment array already
        // handled it.
        if (state.lastCommentStart >= start) {
            return;
        }
        state.lastCommentStart = start;

        comment = {
            type: type,
            value: value
        };
        if (extra.range) {
            comment.range = [start, end];
        }
        if (extra.loc) {
            comment.loc = loc;
        }
        extra.comments.push(comment);
        if (extra.attachComment) {
            extra.leadingComments.push(comment);
            extra.trailingComments.push(comment);
        }
    }

    function scanComment() {
        var comment, ch, loc, start, blockComment, lineComment;

        comment = '';
        blockComment = false;
        lineComment = false;

        while (index < length) {
            ch = source[index];

            if (lineComment) {
                ch = source[index++];
                if (isLineTerminator(ch.charCodeAt(0))) {
                    loc.end = {
                        line: lineNumber,
                        column: index - lineStart - 1
                    };
                    lineComment = false;
                    addComment('Line', comment, start, index - 1, loc);
                    if (ch === '\r' && source[index] === '\n') {
                        ++index;
                    }
                    ++lineNumber;
                    lineStart = index;
                    comment = '';
                } else if (index >= length) {
                    lineComment = false;
                    comment += ch;
                    loc.end = {
                        line: lineNumber,
                        column: length - lineStart
                    };
                    addComment('Line', comment, start, length, loc);
                } else {
                    comment += ch;
                }
            } else if (blockComment) {
                if (isLineTerminator(ch.charCodeAt(0))) {
                    if (ch === '\r') {
                        ++index;
                        comment += '\r';
                    }
                    if (ch !== '\r' || source[index] === '\n') {
                        comment += source[index];
                        ++lineNumber;
                        ++index;
                        lineStart = index;
                        if (index >= length) {
                            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
                        }
                    }
                } else {
                    ch = source[index++];
                    if (index >= length) {
                        throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
                    }
                    comment += ch;
                    if (ch === '*') {
                        ch = source[index];
                        if (ch === '/') {
                            comment = comment.substr(0, comment.length - 1);
                            blockComment = false;
                            ++index;
                            loc.end = {
                                line: lineNumber,
                                column: index - lineStart
                            };
                            addComment('Block', comment, start, index, loc);
                            comment = '';
                        }
                    }
                }
            } else if (ch === '/') {
                ch = source[index + 1];
                if (ch === '/') {
                    loc = {
                        start: {
                            line: lineNumber,
                            column: index - lineStart
                        }
                    };
                    start = index;
                    index += 2;
                    lineComment = true;
                    if (index >= length) {
                        loc.end = {
                            line: lineNumber,
                            column: index - lineStart
                        };
                        lineComment = false;
                        addComment('Line', comment, start, index, loc);
                    }
                } else if (ch === '*') {
                    start = index;
                    index += 2;
                    blockComment = true;
                    loc = {
                        start: {
                            line: lineNumber,
                            column: index - lineStart - 2
                        }
                    };
                    if (index >= length) {
                        throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
                    }
                } else {
                    break;
                }
            } else if (isWhiteSpace(ch.charCodeAt(0))) {
                ++index;
            } else if (isLineTerminator(ch.charCodeAt(0))) {
                ++index;
                if (ch ===  '\r' && source[index] === '\n') {
                    ++index;
                }
                ++lineNumber;
                lineStart = index;
            } else {
                break;
            }
        }
    }

    // 16 XJS

    XHTMLEntities = {
        quot: '\u0022',
        amp: '&',
        apos: '\u0027',
        lt: '<',
        gt: '>',
        nbsp: '\u00A0',
        iexcl: '\u00A1',
        cent: '\u00A2',
        pound: '\u00A3',
        curren: '\u00A4',
        yen: '\u00A5',
        brvbar: '\u00A6',
        sect: '\u00A7',
        uml: '\u00A8',
        copy: '\u00A9',
        ordf: '\u00AA',
        laquo: '\u00AB',
        not: '\u00AC',
        shy: '\u00AD',
        reg: '\u00AE',
        macr: '\u00AF',
        deg: '\u00B0',
        plusmn: '\u00B1',
        sup2: '\u00B2',
        sup3: '\u00B3',
        acute: '\u00B4',
        micro: '\u00B5',
        para: '\u00B6',
        middot: '\u00B7',
        cedil: '\u00B8',
        sup1: '\u00B9',
        ordm: '\u00BA',
        raquo: '\u00BB',
        frac14: '\u00BC',
        frac12: '\u00BD',
        frac34: '\u00BE',
        iquest: '\u00BF',
        Agrave: '\u00C0',
        Aacute: '\u00C1',
        Acirc: '\u00C2',
        Atilde: '\u00C3',
        Auml: '\u00C4',
        Aring: '\u00C5',
        AElig: '\u00C6',
        Ccedil: '\u00C7',
        Egrave: '\u00C8',
        Eacute: '\u00C9',
        Ecirc: '\u00CA',
        Euml: '\u00CB',
        Igrave: '\u00CC',
        Iacute: '\u00CD',
        Icirc: '\u00CE',
        Iuml: '\u00CF',
        ETH: '\u00D0',
        Ntilde: '\u00D1',
        Ograve: '\u00D2',
        Oacute: '\u00D3',
        Ocirc: '\u00D4',
        Otilde: '\u00D5',
        Ouml: '\u00D6',
        times: '\u00D7',
        Oslash: '\u00D8',
        Ugrave: '\u00D9',
        Uacute: '\u00DA',
        Ucirc: '\u00DB',
        Uuml: '\u00DC',
        Yacute: '\u00DD',
        THORN: '\u00DE',
        szlig: '\u00DF',
        agrave: '\u00E0',
        aacute: '\u00E1',
        acirc: '\u00E2',
        atilde: '\u00E3',
        auml: '\u00E4',
        aring: '\u00E5',
        aelig: '\u00E6',
        ccedil: '\u00E7',
        egrave: '\u00E8',
        eacute: '\u00E9',
        ecirc: '\u00EA',
        euml: '\u00EB',
        igrave: '\u00EC',
        iacute: '\u00ED',
        icirc: '\u00EE',
        iuml: '\u00EF',
        eth: '\u00F0',
        ntilde: '\u00F1',
        ograve: '\u00F2',
        oacute: '\u00F3',
        ocirc: '\u00F4',
        otilde: '\u00F5',
        ouml: '\u00F6',
        divide: '\u00F7',
        oslash: '\u00F8',
        ugrave: '\u00F9',
        uacute: '\u00FA',
        ucirc: '\u00FB',
        uuml: '\u00FC',
        yacute: '\u00FD',
        thorn: '\u00FE',
        yuml: '\u00FF',
        OElig: '\u0152',
        oelig: '\u0153',
        Scaron: '\u0160',
        scaron: '\u0161',
        Yuml: '\u0178',
        fnof: '\u0192',
        circ: '\u02C6',
        tilde: '\u02DC',
        Alpha: '\u0391',
        Beta: '\u0392',
        Gamma: '\u0393',
        Delta: '\u0394',
        Epsilon: '\u0395',
        Zeta: '\u0396',
        Eta: '\u0397',
        Theta: '\u0398',
        Iota: '\u0399',
        Kappa: '\u039A',
        Lambda: '\u039B',
        Mu: '\u039C',
        Nu: '\u039D',
        Xi: '\u039E',
        Omicron: '\u039F',
        Pi: '\u03A0',
        Rho: '\u03A1',
        Sigma: '\u03A3',
        Tau: '\u03A4',
        Upsilon: '\u03A5',
        Phi: '\u03A6',
        Chi: '\u03A7',
        Psi: '\u03A8',
        Omega: '\u03A9',
        alpha: '\u03B1',
        beta: '\u03B2',
        gamma: '\u03B3',
        delta: '\u03B4',
        epsilon: '\u03B5',
        zeta: '\u03B6',
        eta: '\u03B7',
        theta: '\u03B8',
        iota: '\u03B9',
        kappa: '\u03BA',
        lambda: '\u03BB',
        mu: '\u03BC',
        nu: '\u03BD',
        xi: '\u03BE',
        omicron: '\u03BF',
        pi: '\u03C0',
        rho: '\u03C1',
        sigmaf: '\u03C2',
        sigma: '\u03C3',
        tau: '\u03C4',
        upsilon: '\u03C5',
        phi: '\u03C6',
        chi: '\u03C7',
        psi: '\u03C8',
        omega: '\u03C9',
        thetasym: '\u03D1',
        upsih: '\u03D2',
        piv: '\u03D6',
        ensp: '\u2002',
        emsp: '\u2003',
        thinsp: '\u2009',
        zwnj: '\u200C',
        zwj: '\u200D',
        lrm: '\u200E',
        rlm: '\u200F',
        ndash: '\u2013',
        mdash: '\u2014',
        lsquo: '\u2018',
        rsquo: '\u2019',
        sbquo: '\u201A',
        ldquo: '\u201C',
        rdquo: '\u201D',
        bdquo: '\u201E',
        dagger: '\u2020',
        Dagger: '\u2021',
        bull: '\u2022',
        hellip: '\u2026',
        permil: '\u2030',
        prime: '\u2032',
        Prime: '\u2033',
        lsaquo: '\u2039',
        rsaquo: '\u203A',
        oline: '\u203E',
        frasl: '\u2044',
        euro: '\u20AC',
        image: '\u2111',
        weierp: '\u2118',
        real: '\u211C',
        trade: '\u2122',
        alefsym: '\u2135',
        larr: '\u2190',
        uarr: '\u2191',
        rarr: '\u2192',
        darr: '\u2193',
        harr: '\u2194',
        crarr: '\u21B5',
        lArr: '\u21D0',
        uArr: '\u21D1',
        rArr: '\u21D2',
        dArr: '\u21D3',
        hArr: '\u21D4',
        forall: '\u2200',
        part: '\u2202',
        exist: '\u2203',
        empty: '\u2205',
        nabla: '\u2207',
        isin: '\u2208',
        notin: '\u2209',
        ni: '\u220B',
        prod: '\u220F',
        sum: '\u2211',
        minus: '\u2212',
        lowast: '\u2217',
        radic: '\u221A',
        prop: '\u221D',
        infin: '\u221E',
        ang: '\u2220',
        and: '\u2227',
        or: '\u2228',
        cap: '\u2229',
        cup: '\u222A',
        'int': '\u222B',
        there4: '\u2234',
        sim: '\u223C',
        cong: '\u2245',
        asymp: '\u2248',
        ne: '\u2260',
        equiv: '\u2261',
        le: '\u2264',
        ge: '\u2265',
        sub: '\u2282',
        sup: '\u2283',
        nsub: '\u2284',
        sube: '\u2286',
        supe: '\u2287',
        oplus: '\u2295',
        otimes: '\u2297',
        perp: '\u22A5',
        sdot: '\u22C5',
        lceil: '\u2308',
        rceil: '\u2309',
        lfloor: '\u230A',
        rfloor: '\u230B',
        lang: '\u2329',
        rang: '\u232A',
        loz: '\u25CA',
        spades: '\u2660',
        clubs: '\u2663',
        hearts: '\u2665',
        diams: '\u2666'
    };

    function getQualifiedXJSName(object) {
        if (object.type === Syntax.XJSIdentifier) {
            return object.name;
        }
        if (object.type === Syntax.XJSNamespacedName) {
            return object.namespace.name + ':' + object.name.name;
        }
        if (object.type === Syntax.XJSMemberExpression) {
            return (
                getQualifiedXJSName(object.object) + '.' +
                getQualifiedXJSName(object.property)
            );
        }
    }

    function isXJSIdentifierStart(ch) {
        // exclude backslash (\)
        return (ch !== 92) && isIdentifierStart(ch);
    }

    function isXJSIdentifierPart(ch) {
        // exclude backslash (\) and add hyphen (-)
        return (ch !== 92) && (ch === 45 || isIdentifierPart(ch));
    }

    function scanXJSIdentifier() {
        var ch, start, value = '';

        start = index;
        while (index < length) {
            ch = source.charCodeAt(index);
            if (!isXJSIdentifierPart(ch)) {
                break;
            }
            value += source[index++];
        }

        return {
            type: Token.XJSIdentifier,
            value: value,
            lineNumber: lineNumber,
            lineStart: lineStart,
            range: [start, index]
        };
    }

    function scanXJSEntity() {
        var ch, str = '', start = index, count = 0, code;
        ch = source[index];
        assert(ch === '&', 'Entity must start with an ampersand');
        index++;
        while (index < length && count++ < 10) {
            ch = source[index++];
            if (ch === ';') {
                break;
            }
            str += ch;
        }

        // Well-formed entity (ending was found).
        if (ch === ';') {
            // Numeric entity.
            if (str[0] === '#') {
                if (str[1] === 'x') {
                    code = +('0' + str.substr(1));
                } else {
                    // Removing leading zeros in order to avoid treating as octal in old browsers.
                    code = +str.substr(1).replace(Regex.LeadingZeros, '');
                }

                if (!isNaN(code)) {
                    return String.fromCharCode(code);
                }
            } else if (XHTMLEntities[str]) {
                return XHTMLEntities[str];
            }
        }

        // Treat non-entity sequences as regular text.
        index = start + 1;
        return '&';
    }

    function scanXJSText(stopChars) {
        var ch, str = '', start;
        start = index;
        while (index < length) {
            ch = source[index];
            if (stopChars.indexOf(ch) !== -1) {
                break;
            }
            if (ch === '&') {
                str += scanXJSEntity();
            } else {
                index++;
                if (ch === '\r' && source[index] === '\n') {
                    str += ch;
                    ch = source[index];
                    index++;
                }
                if (isLineTerminator(ch.charCodeAt(0))) {
                    ++lineNumber;
                    lineStart = index;
                }
                str += ch;
            }
        }
        return {
            type: Token.XJSText,
            value: str,
            lineNumber: lineNumber,
            lineStart: lineStart,
            range: [start, index]
        };
    }

    function scanXJSStringLiteral() {
        var innerToken, quote, start;

        quote = source[index];
        assert((quote === '\'' || quote === '"'),
            'String literal must starts with a quote');

        start = index;
        ++index;

        innerToken = scanXJSText([quote]);

        if (quote !== source[index]) {
            throwError({}, Messages.UnexpectedToken, 'ILLEGAL');
        }

        ++index;

        innerToken.range = [start, index];

        return innerToken;
    }

    /**
     * Between XJS opening and closing tags (e.g. <foo>HERE</foo>), anything that
     * is not another XJS tag and is not an expression wrapped by {} is text.
     */
    function advanceXJSChild() {
        var ch = source.charCodeAt(index);

        // { (123) and < (60)
        if (ch !== 123 && ch !== 60) {
            return scanXJSText(['<', '{']);
        }

        return scanPunctuator();
    }

    function parseXJSIdentifier() {
        var token, marker = markerCreate();

        if (lookahead.type !== Token.XJSIdentifier) {
            throwUnexpected(lookahead);
        }

        token = lex();
        return markerApply(marker, delegate.createXJSIdentifier(token.value));
    }

    function parseXJSNamespacedName() {
        var namespace, name, marker = markerCreate();

        namespace = parseXJSIdentifier();
        expect(':');
        name = parseXJSIdentifier();

        return markerApply(marker, delegate.createXJSNamespacedName(namespace, name));
    }

    function parseXJSMemberExpression() {
        var marker = markerCreate(),
            expr = parseXJSIdentifier();

        while (match('.')) {
            lex();
            expr = markerApply(marker, delegate.createXJSMemberExpression(expr, parseXJSIdentifier()));
        }

        return expr;
    }

    function parseXJSElementName() {
        if (lookahead2().value === ':') {
            return parseXJSNamespacedName();
        }
        if (lookahead2().value === '.') {
            return parseXJSMemberExpression();
        }

        return parseXJSIdentifier();
    }

    function parseXJSAttributeName() {
        if (lookahead2().value === ':') {
            return parseXJSNamespacedName();
        }

        return parseXJSIdentifier();
    }

    function parseXJSAttributeValue() {
        var value, marker;
        if (match('{')) {
            value = parseXJSExpressionContainer();
            if (value.expression.type === Syntax.XJSEmptyExpression) {
                throwError(
                    value,
                    'XJS attributes must only be assigned a non-empty ' +
                        'expression'
                );
            }
        } else if (match('<')) {
            value = parseXJSElement();
        } else if (lookahead.type === Token.XJSText) {
            marker = markerCreate();
            value = markerApply(marker, delegate.createLiteral(lex()));
        } else {
            throwError({}, Messages.InvalidXJSAttributeValue);
        }
        return value;
    }

    function parseXJSEmptyExpression() {
        var marker = markerCreatePreserveWhitespace();
        while (source.charAt(index) !== '}') {
            index++;
        }
        return markerApply(marker, delegate.createXJSEmptyExpression());
    }

    function parseXJSExpressionContainer() {
        var expression, origInXJSChild, origInXJSTag, marker = markerCreate();

        origInXJSChild = state.inXJSChild;
        origInXJSTag = state.inXJSTag;
        state.inXJSChild = false;
        state.inXJSTag = false;

        expect('{');

        if (match('}')) {
            expression = parseXJSEmptyExpression();
        } else {
            expression = parseExpression();
        }

        state.inXJSChild = origInXJSChild;
        state.inXJSTag = origInXJSTag;

        expect('}');

        return markerApply(marker, delegate.createXJSExpressionContainer(expression));
    }

    function parseXJSSpreadAttribute() {
        var expression, origInXJSChild, origInXJSTag, marker = markerCreate();

        origInXJSChild = state.inXJSChild;
        origInXJSTag = state.inXJSTag;
        state.inXJSChild = false;
        state.inXJSTag = false;

        expect('{');
        expect('...');

        expression = parseAssignmentExpression();

        state.inXJSChild = origInXJSChild;
        state.inXJSTag = origInXJSTag;

        expect('}');

        return markerApply(marker, delegate.createXJSSpreadAttribute(expression));
    }

    function parseXJSAttribute() {
        var name, marker;

        if (match('{')) {
            return parseXJSSpreadAttribute();
        }

        marker = markerCreate();

        name = parseXJSAttributeName();

        // HTML empty attribute
        if (match('=')) {
            lex();
            return markerApply(marker, delegate.createXJSAttribute(name, parseXJSAttributeValue()));
        }

        return markerApply(marker, delegate.createXJSAttribute(name));
    }

    function parseXJSChild() {
        var token, marker;
        if (match('{')) {
            token = parseXJSExpressionContainer();
        } else if (lookahead.type === Token.XJSText) {
            marker = markerCreatePreserveWhitespace();
            token = markerApply(marker, delegate.createLiteral(lex()));
        } else {
            token = parseXJSElement();
        }
        return token;
    }

    function parseXJSClosingElement() {
        var name, origInXJSChild, origInXJSTag, marker = markerCreate();
        origInXJSChild = state.inXJSChild;
        origInXJSTag = state.inXJSTag;
        state.inXJSChild = false;
        state.inXJSTag = true;
        expect('<');
        expect('/');
        name = parseXJSElementName();
        // Because advance() (called by lex() called by expect()) expects there
        // to be a valid token after >, it needs to know whether to look for a
        // standard JS token or an XJS text node
        state.inXJSChild = origInXJSChild;
        state.inXJSTag = origInXJSTag;
        expect('>');
        return markerApply(marker, delegate.createXJSClosingElement(name));
    }

    function parseXJSOpeningElement() {
        var name, attribute, attributes = [], selfClosing = false, origInXJSChild, origInXJSTag, marker = markerCreate();

        origInXJSChild = state.inXJSChild;
        origInXJSTag = state.inXJSTag;
        state.inXJSChild = false;
        state.inXJSTag = true;

        expect('<');

        name = parseXJSElementName();

        while (index < length &&
                lookahead.value !== '/' &&
                lookahead.value !== '>') {
            attributes.push(parseXJSAttribute());
        }

        state.inXJSTag = origInXJSTag;

        if (lookahead.value === '/') {
            expect('/');
            // Because advance() (called by lex() called by expect()) expects
            // there to be a valid token after >, it needs to know whether to
            // look for a standard JS token or an XJS text node
            state.inXJSChild = origInXJSChild;
            expect('>');
            selfClosing = true;
        } else {
            state.inXJSChild = true;
            expect('>');
        }
        return markerApply(marker, delegate.createXJSOpeningElement(name, attributes, selfClosing));
    }

    function parseXJSElement() {
        var openingElement, closingElement = null, children = [], origInXJSChild, origInXJSTag, marker = markerCreate();

        origInXJSChild = state.inXJSChild;
        origInXJSTag = state.inXJSTag;
        openingElement = parseXJSOpeningElement();

        if (!openingElement.selfClosing) {
            while (index < length) {
                state.inXJSChild = false; // Call lookahead2() with inXJSChild = false because </ should not be considered in the child
                if (lookahead.value === '<' && lookahead2().value === '/') {
                    break;
                }
                state.inXJSChild = true;
                children.push(parseXJSChild());
            }
            state.inXJSChild = origInXJSChild;
            state.inXJSTag = origInXJSTag;
            closingElement = parseXJSClosingElement();
            if (getQualifiedXJSName(closingElement.name) !== getQualifiedXJSName(openingElement.name)) {
                throwError({}, Messages.ExpectedXJSClosingTag, getQualifiedXJSName(openingElement.name));
            }
        }

        // When (erroneously) writing two adjacent tags like
        //
        //     var x = <div>one</div><div>two</div>;
        //
        // the default error message is a bit incomprehensible. Since it's
        // rarely (never?) useful to write a less-than sign after an XJS
        // element, we disallow it here in the parser in order to provide a
        // better error message. (In the rare case that the less-than operator
        // was intended, the left tag can be wrapped in parentheses.)
        if (!origInXJSChild && match('<')) {
            throwError(lookahead, Messages.AdjacentXJSElements);
        }

        return markerApply(marker, delegate.createXJSElement(openingElement, closingElement, children));
    }

    function collectToken() {
        var start, loc, token, range, value, entry;

        if (!state.inXJSChild) {
            skipComment();
        }

        start = index;
        loc = {
            start: {
                line: lineNumber,
                column: index - lineStart
            }
        };

        token = extra.advance();
        loc.end = {
            line: lineNumber,
            column: index - lineStart
        };

        if (token.type !== Token.EOF) {
            range = [token.range[0], token.range[1]];
            value = source.slice(token.range[0], token.range[1]);
            entry = {
                type: TokenName[token.type],
                value: value,
                range: range,
                loc: loc
            };
            if (token.regex) {
                entry.regex = {
                    pattern: token.regex.pattern,
                    flags: token.regex.flags
                };
            }
            extra.tokens.push(entry);
        }

        return token;
    }

    function collectRegex() {
        var pos, loc, regex, token;

        skipComment();

        pos = index;
        loc = {
            start: {
                line: lineNumber,
                column: index - lineStart
            }
        };

        regex = extra.scanRegExp();
        loc.end = {
            line: lineNumber,
            column: index - lineStart
        };

        if (!extra.tokenize) {
            // Pop the previous token, which is likely '/' or '/='
            if (extra.tokens.length > 0) {
                token = extra.tokens[extra.tokens.length - 1];
                if (token.range[0] === pos && token.type === 'Punctuator') {
                    if (token.value === '/' || token.value === '/=') {
                        extra.tokens.pop();
                    }
                }
            }

            extra.tokens.push({
                type: 'RegularExpression',
                value: regex.literal,
                regex: regex.regex,
                range: [pos, index],
                loc: loc
            });
        }

        return regex;
    }

    function filterTokenLocation() {
        var i, entry, token, tokens = [];

        for (i = 0; i < extra.tokens.length; ++i) {
            entry = extra.tokens[i];
            token = {
                type: entry.type,
                value: entry.value
            };
            if (entry.regex) {
                token.regex = {
                    pattern: entry.regex.pattern,
                    flags: entry.regex.flags
                };
            }
            if (extra.range) {
                token.range = entry.range;
            }
            if (extra.loc) {
                token.loc = entry.loc;
            }
            tokens.push(token);
        }

        extra.tokens = tokens;
    }

    function patch() {
        if (extra.comments) {
            extra.skipComment = skipComment;
            skipComment = scanComment;
        }

        if (typeof extra.tokens !== 'undefined') {
            extra.advance = advance;
            extra.scanRegExp = scanRegExp;

            advance = collectToken;
            scanRegExp = collectRegex;
        }
    }

    function unpatch() {
        if (typeof extra.skipComment === 'function') {
            skipComment = extra.skipComment;
        }

        if (typeof extra.scanRegExp === 'function') {
            advance = extra.advance;
            scanRegExp = extra.scanRegExp;
        }
    }

    // This is used to modify the delegate.

    function extend(object, properties) {
        var entry, result = {};

        for (entry in object) {
            if (object.hasOwnProperty(entry)) {
                result[entry] = object[entry];
            }
        }

        for (entry in properties) {
            if (properties.hasOwnProperty(entry)) {
                result[entry] = properties[entry];
            }
        }

        return result;
    }

    function tokenize(code, options) {
        var toString,
            token,
            tokens;

        toString = String;
        if (typeof code !== 'string' && !(code instanceof String)) {
            code = toString(code);
        }

        delegate = SyntaxTreeDelegate;
        source = code;
        index = 0;
        lineNumber = (source.length > 0) ? 1 : 0;
        lineStart = 0;
        length = source.length;
        lookahead = null;
        state = {
            allowKeyword: true,
            allowIn: true,
            labelSet: {},
            inFunctionBody: false,
            inIteration: false,
            inSwitch: false,
            lastCommentStart: -1
        };

        extra = {};

        // Options matching.
        options = options || {};

        // Of course we collect tokens here.
        options.tokens = true;
        extra.tokens = [];
        extra.tokenize = true;
        // The following two fields are necessary to compute the Regex tokens.
        extra.openParenToken = -1;
        extra.openCurlyToken = -1;

        extra.range = (typeof options.range === 'boolean') && options.range;
        extra.loc = (typeof options.loc === 'boolean') && options.loc;

        if (typeof options.comment === 'boolean' && options.comment) {
            extra.comments = [];
        }
        if (typeof options.tolerant === 'boolean' && options.tolerant) {
            extra.errors = [];
        }

        if (length > 0) {
            if (typeof source[0] === 'undefined') {
                // Try first to convert to a string. This is good as fast path
                // for old IE which understands string indexing for string
                // literals only and not for string object.
                if (code instanceof String) {
                    source = code.valueOf();
                }
            }
        }

        patch();

        try {
            peek();
            if (lookahead.type === Token.EOF) {
                return extra.tokens;
            }

            token = lex();
            while (lookahead.type !== Token.EOF) {
                try {
                    token = lex();
                } catch (lexError) {
                    token = lookahead;
                    if (extra.errors) {
                        extra.errors.push(lexError);
                        // We have to break on the first error
                        // to avoid infinite loops.
                        break;
                    } else {
                        throw lexError;
                    }
                }
            }

            filterTokenLocation();
            tokens = extra.tokens;
            if (typeof extra.comments !== 'undefined') {
                tokens.comments = extra.comments;
            }
            if (typeof extra.errors !== 'undefined') {
                tokens.errors = extra.errors;
            }
        } catch (e) {
            throw e;
        } finally {
            unpatch();
            extra = {};
        }
        return tokens;
    }

    function parse(code, options) {
        var program, toString;

        toString = String;
        if (typeof code !== 'string' && !(code instanceof String)) {
            code = toString(code);
        }

        delegate = SyntaxTreeDelegate;
        source = code;
        index = 0;
        lineNumber = (source.length > 0) ? 1 : 0;
        lineStart = 0;
        length = source.length;
        lookahead = null;
        state = {
            allowKeyword: false,
            allowIn: true,
            labelSet: {},
            parenthesizedCount: 0,
            inFunctionBody: false,
            inIteration: false,
            inSwitch: false,
            inXJSChild: false,
            inXJSTag: false,
            lastCommentStart: -1,
            yieldAllowed: false,
            awaitAllowed: false
        };

        extra = {};
        if (typeof options !== 'undefined') {
            extra.range = (typeof options.range === 'boolean') && options.range;
            extra.loc = (typeof options.loc === 'boolean') && options.loc;
            extra.attachComment = (typeof options.attachComment === 'boolean') && options.attachComment;

            if (extra.loc && options.source !== null && options.source !== undefined) {
                delegate = extend(delegate, {
                    'postProcess': function (node) {
                        node.loc.source = toString(options.source);
                        return node;
                    }
                });
            }

            if (typeof options.tokens === 'boolean' && options.tokens) {
                extra.tokens = [];
            }
            if (typeof options.comment === 'boolean' && options.comment) {
                extra.comments = [];
            }
            if (typeof options.tolerant === 'boolean' && options.tolerant) {
                extra.errors = [];
            }
            if (extra.attachComment) {
                extra.range = true;
                extra.comments = [];
                extra.bottomRightStack = [];
                extra.trailingComments = [];
                extra.leadingComments = [];
            }
        }

        if (length > 0) {
            if (typeof source[0] === 'undefined') {
                // Try first to convert to a string. This is good as fast path
                // for old IE which understands string indexing for string
                // literals only and not for string object.
                if (code instanceof String) {
                    source = code.valueOf();
                }
            }
        }

        patch();
        try {
            program = parseProgram();
            if (typeof extra.comments !== 'undefined') {
                program.comments = extra.comments;
            }
            if (typeof extra.tokens !== 'undefined') {
                filterTokenLocation();
                program.tokens = extra.tokens;
            }
            if (typeof extra.errors !== 'undefined') {
                program.errors = extra.errors;
            }
        } catch (e) {
            throw e;
        } finally {
            unpatch();
            extra = {};
        }

        return program;
    }

    // Sync with *.json manifests.
    exports.version = '7001.0001.0000-dev-harmony-fb';

    exports.tokenize = tokenize;

    exports.parse = parse;

    // Deep copy.
    exports.Syntax = (function () {
        var name, types = {};

        if (typeof Object.create === 'function') {
            types = Object.create(null);
        }

        for (name in Syntax) {
            if (Syntax.hasOwnProperty(name)) {
                types[name] = Syntax[name];
            }
        }

        if (typeof Object.freeze === 'function') {
            Object.freeze(types);
        }

        return types;
    }());

}));
/* vim: set sw=4 ts=4 et tw=80 : */