(function (global, factory) {
	typeof exports === 'object' && typeof module !== 'undefined' ? module.exports = factory() :
	typeof define === 'function' && define.amd ? define('GOVUKFrontend.Checkboxes', factory) :
	(global.GOVUKFrontend = global.GOVUKFrontend || {}, global.GOVUKFrontend.Checkboxes = factory());
}(this, (function () { 'use strict';

(function(undefined) {

// Detection from https://github.com/Financial-Times/polyfill-service/blob/master/packages/polyfill-library/polyfills/Object/defineProperty/detect.js
var detect = (
  // In IE8, defineProperty could only act on DOM elements, so full support
  // for the feature requires the ability to set a property on an arbitrary object
  'defineProperty' in Object && (function() {
  	try {
  		var a = {};
  		Object.defineProperty(a, 'test', {value:42});
  		return true;
  	} catch(e) {
  		return false
  	}
  }())
);

if (detect) return

// Polyfill from https://cdn.polyfill.io/v2/polyfill.js?features=Object.defineProperty&flags=always
(function (nativeDefineProperty) {

	var supportsAccessors = Object.prototype.hasOwnProperty('__defineGetter__');
	var ERR_ACCESSORS_NOT_SUPPORTED = 'Getters & setters cannot be defined on this javascript engine';
	var ERR_VALUE_ACCESSORS = 'A property cannot both have accessors and be writable or have a value';

	Object.defineProperty = function defineProperty(object, property, descriptor) {

		// Where native support exists, assume it
		if (nativeDefineProperty && (object === window || object === document || object === Element.prototype || object instanceof Element)) {
			return nativeDefineProperty(object, property, descriptor);
		}

		if (object === null || !(object instanceof Object || typeof object === 'object')) {
			throw new TypeError('Object.defineProperty called on non-object');
		}

		if (!(descriptor instanceof Object)) {
			throw new TypeError('Property description must be an object');
		}

		var propertyString = String(property);
		var hasValueOrWritable = 'value' in descriptor || 'writable' in descriptor;
		var getterType = 'get' in descriptor && typeof descriptor.get;
		var setterType = 'set' in descriptor && typeof descriptor.set;

		// handle descriptor.get
		if (getterType) {
			if (getterType !== 'function') {
				throw new TypeError('Getter must be a function');
			}
			if (!supportsAccessors) {
				throw new TypeError(ERR_ACCESSORS_NOT_SUPPORTED);
			}
			if (hasValueOrWritable) {
				throw new TypeError(ERR_VALUE_ACCESSORS);
			}
			Object.__defineGetter__.call(object, propertyString, descriptor.get);
		} else {
			object[propertyString] = descriptor.value;
		}

		// handle descriptor.set
		if (setterType) {
			if (setterType !== 'function') {
				throw new TypeError('Setter must be a function');
			}
			if (!supportsAccessors) {
				throw new TypeError(ERR_ACCESSORS_NOT_SUPPORTED);
			}
			if (hasValueOrWritable) {
				throw new TypeError(ERR_VALUE_ACCESSORS);
			}
			Object.__defineSetter__.call(object, propertyString, descriptor.set);
		}

		// OK to define value unconditionally - if a getter has been specified as well, an error would be thrown above
		if ('value' in descriptor) {
			object[propertyString] = descriptor.value;
		}

		return object;
	};
}(Object.defineProperty));
})
.call('object' === typeof window && window || 'object' === typeof self && self || 'object' === typeof global && global || {});

(function(undefined) {
  // Detection from https://github.com/Financial-Times/polyfill-service/blob/master/packages/polyfill-library/polyfills/Function/prototype/bind/detect.js
  var detect = 'bind' in Function.prototype;

  if (detect) return

  // Polyfill from https://cdn.polyfill.io/v2/polyfill.js?features=Function.prototype.bind&flags=always
  Object.defineProperty(Function.prototype, 'bind', {
      value: function bind(that) { // .length is 1
          // add necessary es5-shim utilities
          var $Array = Array;
          var $Object = Object;
          var ObjectPrototype = $Object.prototype;
          var ArrayPrototype = $Array.prototype;
          var Empty = function Empty() {};
          var to_string = ObjectPrototype.toString;
          var hasToStringTag = typeof Symbol === 'function' && typeof Symbol.toStringTag === 'symbol';
          var isCallable; /* inlined from https://npmjs.com/is-callable */ var fnToStr = Function.prototype.toString, tryFunctionObject = function tryFunctionObject(value) { try { fnToStr.call(value); return true; } catch (e) { return false; } }, fnClass = '[object Function]', genClass = '[object GeneratorFunction]'; isCallable = function isCallable(value) { if (typeof value !== 'function') { return false; } if (hasToStringTag) { return tryFunctionObject(value); } var strClass = to_string.call(value); return strClass === fnClass || strClass === genClass; };
          var array_slice = ArrayPrototype.slice;
          var array_concat = ArrayPrototype.concat;
          var array_push = ArrayPrototype.push;
          var max = Math.max;
          // /add necessary es5-shim utilities

          // 1. Let Target be the this value.
          var target = this;
          // 2. If IsCallable(Target) is false, throw a TypeError exception.
          if (!isCallable(target)) {
              throw new TypeError('Function.prototype.bind called on incompatible ' + target);
          }
          // 3. Let A be a new (possibly empty) internal list of all of the
          //   argument values provided after thisArg (arg1, arg2 etc), in order.
          // XXX slicedArgs will stand in for "A" if used
          var args = array_slice.call(arguments, 1); // for normal call
          // 4. Let F be a new native ECMAScript object.
          // 11. Set the [[Prototype]] internal property of F to the standard
          //   built-in Function prototype object as specified in 15.3.3.1.
          // 12. Set the [[Call]] internal property of F as described in
          //   15.3.4.5.1.
          // 13. Set the [[Construct]] internal property of F as described in
          //   15.3.4.5.2.
          // 14. Set the [[HasInstance]] internal property of F as described in
          //   15.3.4.5.3.
          var bound;
          var binder = function () {

              if (this instanceof bound) {
                  // 15.3.4.5.2 [[Construct]]
                  // When the [[Construct]] internal method of a function object,
                  // F that was created using the bind function is called with a
                  // list of arguments ExtraArgs, the following steps are taken:
                  // 1. Let target be the value of F's [[TargetFunction]]
                  //   internal property.
                  // 2. If target has no [[Construct]] internal method, a
                  //   TypeError exception is thrown.
                  // 3. Let boundArgs be the value of F's [[BoundArgs]] internal
                  //   property.
                  // 4. Let args be a new list containing the same values as the
                  //   list boundArgs in the same order followed by the same
                  //   values as the list ExtraArgs in the same order.
                  // 5. Return the result of calling the [[Construct]] internal
                  //   method of target providing args as the arguments.

                  var result = target.apply(
                      this,
                      array_concat.call(args, array_slice.call(arguments))
                  );
                  if ($Object(result) === result) {
                      return result;
                  }
                  return this;

              } else {
                  // 15.3.4.5.1 [[Call]]
                  // When the [[Call]] internal method of a function object, F,
                  // which was created using the bind function is called with a
                  // this value and a list of arguments ExtraArgs, the following
                  // steps are taken:
                  // 1. Let boundArgs be the value of F's [[BoundArgs]] internal
                  //   property.
                  // 2. Let boundThis be the value of F's [[BoundThis]] internal
                  //   property.
                  // 3. Let target be the value of F's [[TargetFunction]] internal
                  //   property.
                  // 4. Let args be a new list containing the same values as the
                  //   list boundArgs in the same order followed by the same
                  //   values as the list ExtraArgs in the same order.
                  // 5. Return the result of calling the [[Call]] internal method
                  //   of target providing boundThis as the this value and
                  //   providing args as the arguments.

                  // equiv: target.call(this, ...boundArgs, ...args)
                  return target.apply(
                      that,
                      array_concat.call(args, array_slice.call(arguments))
                  );

              }

          };

          // 15. If the [[Class]] internal property of Target is "Function", then
          //     a. Let L be the length property of Target minus the length of A.
          //     b. Set the length own property of F to either 0 or L, whichever is
          //       larger.
          // 16. Else set the length own property of F to 0.

          var boundLength = max(0, target.length - args.length);

          // 17. Set the attributes of the length own property of F to the values
          //   specified in 15.3.5.1.
          var boundArgs = [];
          for (var i = 0; i < boundLength; i++) {
              array_push.call(boundArgs, '$' + i);
          }

          // XXX Build a dynamic function with desired amount of arguments is the only
          // way to set the length property of a function.
          // In environments where Content Security Policies enabled (Chrome extensions,
          // for ex.) all use of eval or Function costructor throws an exception.
          // However in all of these environments Function.prototype.bind exists
          // and so this code will never be executed.
          bound = Function('binder', 'return function (' + boundArgs.join(',') + '){ return binder.apply(this, arguments); }')(binder);

          if (target.prototype) {
              Empty.prototype = target.prototype;
              bound.prototype = new Empty();
              // Clean up dangling references.
              Empty.prototype = null;
          }

          // TODO
          // 18. Set the [[Extensible]] internal property of F to true.

          // TODO
          // 19. Let thrower be the [[ThrowTypeError]] function Object (13.2.3).
          // 20. Call the [[DefineOwnProperty]] internal method of F with
          //   arguments "caller", PropertyDescriptor {[[Get]]: thrower, [[Set]]:
          //   thrower, [[Enumerable]]: false, [[Configurable]]: false}, and
          //   false.
          // 21. Call the [[DefineOwnProperty]] internal method of F with
          //   arguments "arguments", PropertyDescriptor {[[Get]]: thrower,
          //   [[Set]]: thrower, [[Enumerable]]: false, [[Configurable]]: false},
          //   and false.

          // TODO
          // NOTE Function objects created using Function.prototype.bind do not
          // have a prototype property or the [[Code]], [[FormalParameters]], and
          // [[Scope]] internal properties.
          // XXX can't delete prototype in pure-js.

          // 22. Return F.
          return bound;
      }
  });
})
.call('object' === typeof window && window || 'object' === typeof self && self || 'object' === typeof global && global || {});

(function(undefined) {

// Detection from https://github.com/Financial-Times/polyfill-service/blob/master/packages/polyfill-library/polyfills/Window/detect.js
var detect = ('Window' in this);

if (detect) return

// Polyfill from https://cdn.polyfill.io/v2/polyfill.js?features=Window&flags=always
if ((typeof WorkerGlobalScope === "undefined") && (typeof importScripts !== "function")) {
	(function (global) {
		if (global.constructor) {
			global.Window = global.constructor;
		} else {
			(global.Window = global.constructor = new Function('return function Window() {}')()).prototype = this;
		}
	}(this));
}

})
.call('object' === typeof window && window || 'object' === typeof self && self || 'object' === typeof global && global || {});

(function(undefined) {

// Detection from https://github.com/Financial-Times/polyfill-service/blob/master/packages/polyfill-library/polyfills/Document/detect.js
var detect = ("Document" in this);

if (detect) return

// Polyfill from https://cdn.polyfill.io/v2/polyfill.js?features=Document&flags=always
if ((typeof WorkerGlobalScope === "undefined") && (typeof importScripts !== "function")) {

	if (this.HTMLDocument) { // IE8

		// HTMLDocument is an extension of Document.  If the browser has HTMLDocument but not Document, the former will suffice as an alias for the latter.
		this.Document = this.HTMLDocument;

	} else {

		// Create an empty function to act as the missing constructor for the document object, attach the document object as its prototype.  The function needs to be anonymous else it is hoisted and causes the feature detect to prematurely pass, preventing the assignments below being made.
		this.Document = this.HTMLDocument = document.constructor = (new Function('return function Document() {}')());
		this.Document.prototype = document;
	}
}


})
.call('object' === typeof window && window || 'object' === typeof self && self || 'object' === typeof global && global || {});

(function(undefined) {

// Detection from https://github.com/Financial-Times/polyfill-service/blob/master/packages/polyfill-library/polyfills/Element/detect.js
var detect = ('Element' in this && 'HTMLElement' in this);

if (detect) return

// Polyfill from https://cdn.polyfill.io/v2/polyfill.js?features=Element&flags=always
(function () {

	// IE8
	if (window.Element && !window.HTMLElement) {
		window.HTMLElement = window.Element;
		return;
	}

	// create Element constructor
	window.Element = window.HTMLElement = new Function('return function Element() {}')();

	// generate sandboxed iframe
	var vbody = document.appendChild(document.createElement('body'));
	var frame = vbody.appendChild(document.createElement('iframe'));

	// use sandboxed iframe to replicate Element functionality
	var frameDocument = frame.contentWindow.document;
	var prototype = Element.prototype = frameDocument.appendChild(frameDocument.createElement('*'));
	var cache = {};

	// polyfill Element.prototype on an element
	var shiv = function (element, deep) {
		var
		childNodes = element.childNodes || [],
		index = -1,
		key, value, childNode;

		if (element.nodeType === 1 && element.constructor !== Element) {
			element.constructor = Element;

			for (key in cache) {
				value = cache[key];
				element[key] = value;
			}
		}

		while (childNode = deep && childNodes[++index]) {
			shiv(childNode, deep);
		}

		return element;
	};

	var elements = document.getElementsByTagName('*');
	var nativeCreateElement = document.createElement;
	var interval;
	var loopLimit = 100;

	prototype.attachEvent('onpropertychange', function (event) {
		var
		propertyName = event.propertyName,
		nonValue = !cache.hasOwnProperty(propertyName),
		newValue = prototype[propertyName],
		oldValue = cache[propertyName],
		index = -1,
		element;

		while (element = elements[++index]) {
			if (element.nodeType === 1) {
				if (nonValue || element[propertyName] === oldValue) {
					element[propertyName] = newValue;
				}
			}
		}

		cache[propertyName] = newValue;
	});

	prototype.constructor = Element;

	if (!prototype.hasAttribute) {
		// <Element>.hasAttribute
		prototype.hasAttribute = function hasAttribute(name) {
			return this.getAttribute(name) !== null;
		};
	}

	// Apply Element prototype to the pre-existing DOM as soon as the body element appears.
	function bodyCheck() {
		if (!(loopLimit--)) clearTimeout(interval);
		if (document.body && !document.body.prototype && /(complete|interactive)/.test(document.readyState)) {
			shiv(document, true);
			if (interval && document.body.prototype) clearTimeout(interval);
			return (!!document.body.prototype);
		}
		return false;
	}
	if (!bodyCheck()) {
		document.onreadystatechange = bodyCheck;
		interval = setInterval(bodyCheck, 25);
	}

	// Apply to any new elements created after load
	document.createElement = function createElement(nodeName) {
		var element = nativeCreateElement(String(nodeName).toLowerCase());
		return shiv(element);
	};

	// remove sandboxed iframe
	document.removeChild(vbody);
}());

})
.call('object' === typeof window && window || 'object' === typeof self && self || 'object' === typeof global && global || {});

(function(undefined) {

// Detection from https://github.com/Financial-Times/polyfill-service/blob/master/packages/polyfill-library/polyfills/Event/detect.js
var detect = (
  (function(global) {

  	if (!('Event' in global)) return false;
  	if (typeof global.Event === 'function') return true;

  	try {

  		// In IE 9-11, the Event object exists but cannot be instantiated
  		new Event('click');
  		return true;
  	} catch(e) {
  		return false;
  	}
  }(this))
);

if (detect) return

// Polyfill from https://cdn.polyfill.io/v2/polyfill.js?features=Event&flags=always
(function () {
	var unlistenableWindowEvents = {
		click: 1,
		dblclick: 1,
		keyup: 1,
		keypress: 1,
		keydown: 1,
		mousedown: 1,
		mouseup: 1,
		mousemove: 1,
		mouseover: 1,
		mouseenter: 1,
		mouseleave: 1,
		mouseout: 1,
		storage: 1,
		storagecommit: 1,
		textinput: 1
	};

	// This polyfill depends on availability of `document` so will not run in a worker
	// However, we asssume there are no browsers with worker support that lack proper
	// support for `Event` within the worker
	if (typeof document === 'undefined' || typeof window === 'undefined') return;

	function indexOf(array, element) {
		var
		index = -1,
		length = array.length;

		while (++index < length) {
			if (index in array && array[index] === element) {
				return index;
			}
		}

		return -1;
	}

	var existingProto = (window.Event && window.Event.prototype) || null;
	window.Event = Window.prototype.Event = function Event(type, eventInitDict) {
		if (!type) {
			throw new Error('Not enough arguments');
		}

		var event;
		// Shortcut if browser supports createEvent
		if ('createEvent' in document) {
			event = document.createEvent('Event');
			var bubbles = eventInitDict && eventInitDict.bubbles !== undefined ? eventInitDict.bubbles : false;
			var cancelable = eventInitDict && eventInitDict.cancelable !== undefined ? eventInitDict.cancelable : false;

			event.initEvent(type, bubbles, cancelable);

			return event;
		}

		event = document.createEventObject();

		event.type = type;
		event.bubbles = eventInitDict && eventInitDict.bubbles !== undefined ? eventInitDict.bubbles : false;
		event.cancelable = eventInitDict && eventInitDict.cancelable !== undefined ? eventInitDict.cancelable : false;

		return event;
	};
	if (existingProto) {
		Object.defineProperty(window.Event, 'prototype', {
			configurable: false,
			enumerable: false,
			writable: true,
			value: existingProto
		});
	}

	if (!('createEvent' in document)) {
		window.addEventListener = Window.prototype.addEventListener = Document.prototype.addEventListener = Element.prototype.addEventListener = function addEventListener() {
			var
			element = this,
			type = arguments[0],
			listener = arguments[1];

			if (element === window && type in unlistenableWindowEvents) {
				throw new Error('In IE8 the event: ' + type + ' is not available on the window object. Please see https://github.com/Financial-Times/polyfill-service/issues/317 for more information.');
			}

			if (!element._events) {
				element._events = {};
			}

			if (!element._events[type]) {
				element._events[type] = function (event) {
					var
					list = element._events[event.type].list,
					events = list.slice(),
					index = -1,
					length = events.length,
					eventElement;

					event.preventDefault = function preventDefault() {
						if (event.cancelable !== false) {
							event.returnValue = false;
						}
					};

					event.stopPropagation = function stopPropagation() {
						event.cancelBubble = true;
					};

					event.stopImmediatePropagation = function stopImmediatePropagation() {
						event.cancelBubble = true;
						event.cancelImmediate = true;
					};

					event.currentTarget = element;
					event.relatedTarget = event.fromElement || null;
					event.target = event.target || event.srcElement || element;
					event.timeStamp = new Date().getTime();

					if (event.clientX) {
						event.pageX = event.clientX + document.documentElement.scrollLeft;
						event.pageY = event.clientY + document.documentElement.scrollTop;
					}

					while (++index < length && !event.cancelImmediate) {
						if (index in events) {
							eventElement = events[index];

							if (indexOf(list, eventElement) !== -1 && typeof eventElement === 'function') {
								eventElement.call(element, event);
							}
						}
					}
				};

				element._events[type].list = [];

				if (element.attachEvent) {
					element.attachEvent('on' + type, element._events[type]);
				}
			}

			element._events[type].list.push(listener);
		};

		window.removeEventListener = Window.prototype.removeEventListener = Document.prototype.removeEventListener = Element.prototype.removeEventListener = function removeEventListener() {
			var
			element = this,
			type = arguments[0],
			listener = arguments[1],
			index;

			if (element._events && element._events[type] && element._events[type].list) {
				index = indexOf(element._events[type].list, listener);

				if (index !== -1) {
					element._events[type].list.splice(index, 1);

					if (!element._events[type].list.length) {
						if (element.detachEvent) {
							element.detachEvent('on' + type, element._events[type]);
						}
						delete element._events[type];
					}
				}
			}
		};

		window.dispatchEvent = Window.prototype.dispatchEvent = Document.prototype.dispatchEvent = Element.prototype.dispatchEvent = function dispatchEvent(event) {
			if (!arguments.length) {
				throw new Error('Not enough arguments');
			}

			if (!event || typeof event.type !== 'string') {
				throw new Error('DOM Events Exception 0');
			}

			var element = this, type = event.type;

			try {
				if (!event.bubbles) {
					event.cancelBubble = true;

					var cancelBubbleEvent = function (event) {
						event.cancelBubble = true;

						(element || window).detachEvent('on' + type, cancelBubbleEvent);
					};

					this.attachEvent('on' + type, cancelBubbleEvent);
				}

				this.fireEvent('on' + type, event);
			} catch (error) {
				event.target = element;

				do {
					event.currentTarget = element;

					if ('_events' in element && typeof element._events[type] === 'function') {
						element._events[type].call(element, event);
					}

					if (typeof element['on' + type] === 'function') {
						element['on' + type].call(element, event);
					}

					element = element.nodeType === 9 ? element.parentWindow : element.parentNode;
				} while (element && !event.cancelBubble);
			}

			return true;
		};

		// Add the DOMContentLoaded Event
		document.attachEvent('onreadystatechange', function() {
			if (document.readyState === 'complete') {
				document.dispatchEvent(new Event('DOMContentLoaded', {
					bubbles: true
				}));
			}
		});
	}
}());

})
.call('object' === typeof window && window || 'object' === typeof self && self || 'object' === typeof global && global || {});

(function(undefined) {

    // Detection from https://raw.githubusercontent.com/Financial-Times/polyfill-service/master/packages/polyfill-library/polyfills/DOMTokenList/detect.js
    var detect = (
      'DOMTokenList' in this && (function (x) {
        return 'classList' in x ? !x.classList.toggle('x', false) && !x.className : true;
      })(document.createElement('x'))
    );

    if (detect) return

    // Polyfill from https://raw.githubusercontent.com/Financial-Times/polyfill-service/master/packages/polyfill-library/polyfills/DOMTokenList/polyfill.js
    (function (global) {
      var nativeImpl = "DOMTokenList" in global && global.DOMTokenList;

      if (
          !nativeImpl ||
          (
            !!document.createElementNS &&
            !!document.createElementNS('http://www.w3.org/2000/svg', 'svg') &&
            !(document.createElementNS("http://www.w3.org/2000/svg", "svg").classList instanceof DOMTokenList)
          )
        ) {
        global.DOMTokenList = (function() { // eslint-disable-line no-unused-vars
          var dpSupport = true;
          var defineGetter = function (object, name, fn, configurable) {
            if (Object.defineProperty)
              Object.defineProperty(object, name, {
                configurable: false === dpSupport ? true : !!configurable,
                get: fn
              });

            else object.__defineGetter__(name, fn);
          };

          /** Ensure the browser allows Object.defineProperty to be used on native JavaScript objects. */
          try {
            defineGetter({}, "support");
          }
          catch (e) {
            dpSupport = false;
          }


          var _DOMTokenList = function (el, prop) {
            var that = this;
            var tokens = [];
            var tokenMap = {};
            var length = 0;
            var maxLength = 0;
            var addIndexGetter = function (i) {
              defineGetter(that, i, function () {
                preop();
                return tokens[i];
              }, false);

            };
            var reindex = function () {

              /** Define getter functions for array-like access to the tokenList's contents. */
              if (length >= maxLength)
                for (; maxLength < length; ++maxLength) {
                  addIndexGetter(maxLength);
                }
            };

            /** Helper function called at the start of each class method. Internal use only. */
            var preop = function () {
              var error;
              var i;
              var args = arguments;
              var rSpace = /\s+/;

              /** Validate the token/s passed to an instance method, if any. */
              if (args.length)
                for (i = 0; i < args.length; ++i)
                  if (rSpace.test(args[i])) {
                    error = new SyntaxError('String "' + args[i] + '" ' + "contains" + ' an invalid character');
                    error.code = 5;
                    error.name = "InvalidCharacterError";
                    throw error;
                  }


              /** Split the new value apart by whitespace*/
              if (typeof el[prop] === "object") {
                tokens = ("" + el[prop].baseVal).replace(/^\s+|\s+$/g, "").split(rSpace);
              } else {
                tokens = ("" + el[prop]).replace(/^\s+|\s+$/g, "").split(rSpace);
              }

              /** Avoid treating blank strings as single-item token lists */
              if ("" === tokens[0]) tokens = [];

              /** Repopulate the internal token lists */
              tokenMap = {};
              for (i = 0; i < tokens.length; ++i)
                tokenMap[tokens[i]] = true;
              length = tokens.length;
              reindex();
            };

            /** Populate our internal token list if the targeted attribute of the subject element isn't empty. */
            preop();

            /** Return the number of tokens in the underlying string. Read-only. */
            defineGetter(that, "length", function () {
              preop();
              return length;
            });

            /** Override the default toString/toLocaleString methods to return a space-delimited list of tokens when typecast. */
            that.toLocaleString =
              that.toString = function () {
                preop();
                return tokens.join(" ");
              };

            that.item = function (idx) {
              preop();
              return tokens[idx];
            };

            that.contains = function (token) {
              preop();
              return !!tokenMap[token];
            };

            that.add = function () {
              preop.apply(that, args = arguments);

              for (var args, token, i = 0, l = args.length; i < l; ++i) {
                token = args[i];
                if (!tokenMap[token]) {
                  tokens.push(token);
                  tokenMap[token] = true;
                }
              }

              /** Update the targeted attribute of the attached element if the token list's changed. */
              if (length !== tokens.length) {
                length = tokens.length >>> 0;
                if (typeof el[prop] === "object") {
                  el[prop].baseVal = tokens.join(" ");
                } else {
                  el[prop] = tokens.join(" ");
                }
                reindex();
              }
            };

            that.remove = function () {
              preop.apply(that, args = arguments);

              /** Build a hash of token names to compare against when recollecting our token list. */
              for (var args, ignore = {}, i = 0, t = []; i < args.length; ++i) {
                ignore[args[i]] = true;
                delete tokenMap[args[i]];
              }

              /** Run through our tokens list and reassign only those that aren't defined in the hash declared above. */
              for (i = 0; i < tokens.length; ++i)
                if (!ignore[tokens[i]]) t.push(tokens[i]);

              tokens = t;
              length = t.length >>> 0;

              /** Update the targeted attribute of the attached element. */
              if (typeof el[prop] === "object") {
                el[prop].baseVal = tokens.join(" ");
              } else {
                el[prop] = tokens.join(" ");
              }
              reindex();
            };

            that.toggle = function (token, force) {
              preop.apply(that, [token]);

              /** Token state's being forced. */
              if (undefined !== force) {
                if (force) {
                  that.add(token);
                  return true;
                } else {
                  that.remove(token);
                  return false;
                }
              }

              /** Token already exists in tokenList. Remove it, and return FALSE. */
              if (tokenMap[token]) {
                that.remove(token);
                return false;
              }

              /** Otherwise, add the token and return TRUE. */
              that.add(token);
              return true;
            };

            return that;
          };

          return _DOMTokenList;
        }());
      }

      // Add second argument to native DOMTokenList.toggle() if necessary
      (function () {
        var e = document.createElement('span');
        if (!('classList' in e)) return;
        e.classList.toggle('x', false);
        if (!e.classList.contains('x')) return;
        e.classList.constructor.prototype.toggle = function toggle(token /*, force*/) {
          var force = arguments[1];
          if (force === undefined) {
            var add = !this.contains(token);
            this[add ? 'add' : 'remove'](token);
            return add;
          }
          force = !!force;
          this[force ? 'add' : 'remove'](token);
          return force;
        };
      }());

      // Add multiple arguments to native DOMTokenList.add() if necessary
      (function () {
        var e = document.createElement('span');
        if (!('classList' in e)) return;
        e.classList.add('a', 'b');
        if (e.classList.contains('b')) return;
        var native = e.classList.constructor.prototype.add;
        e.classList.constructor.prototype.add = function () {
          var args = arguments;
          var l = arguments.length;
          for (var i = 0; i < l; i++) {
            native.call(this, args[i]);
          }
        };
      }());

      // Add multiple arguments to native DOMTokenList.remove() if necessary
      (function () {
        var e = document.createElement('span');
        if (!('classList' in e)) return;
        e.classList.add('a');
        e.classList.add('b');
        e.classList.remove('a', 'b');
        if (!e.classList.contains('b')) return;
        var native = e.classList.constructor.prototype.remove;
        e.classList.constructor.prototype.remove = function () {
          var args = arguments;
          var l = arguments.length;
          for (var i = 0; i < l; i++) {
            native.call(this, args[i]);
          }
        };
      }());

    }(this));

}).call('object' === typeof window && window || 'object' === typeof self && self || 'object' === typeof global && global || {});

(function(undefined) {

    // Detection from https://raw.githubusercontent.com/Financial-Times/polyfill-service/8717a9e04ac7aff99b4980fbedead98036b0929a/packages/polyfill-library/polyfills/Element/prototype/classList/detect.js
    var detect = (
      'document' in this && "classList" in document.documentElement && 'Element' in this && 'classList' in Element.prototype && (function () {
        var e = document.createElement('span');
        e.classList.add('a', 'b');
        return e.classList.contains('b');
      }())
    );

    if (detect) return

    // Polyfill from https://cdn.polyfill.io/v2/polyfill.js?features=Element.prototype.classList&flags=always
    (function (global) {
      var dpSupport = true;
      var defineGetter = function (object, name, fn, configurable) {
        if (Object.defineProperty)
          Object.defineProperty(object, name, {
            configurable: false === dpSupport ? true : !!configurable,
            get: fn
          });

        else object.__defineGetter__(name, fn);
      };
      /** Ensure the browser allows Object.defineProperty to be used on native JavaScript objects. */
      try {
        defineGetter({}, "support");
      }
      catch (e) {
        dpSupport = false;
      }
      /** Polyfills a property with a DOMTokenList */
      var addProp = function (o, name, attr) {

        defineGetter(o.prototype, name, function () {
          var tokenList;

          var THIS = this,

          /** Prevent this from firing twice for some reason. What the hell, IE. */
          gibberishProperty = "__defineGetter__" + "DEFINE_PROPERTY" + name;
          if(THIS[gibberishProperty]) return tokenList;
          THIS[gibberishProperty] = true;

          /**
           * IE8 can't define properties on native JavaScript objects, so we'll use a dumb hack instead.
           *
           * What this is doing is creating a dummy element ("reflection") inside a detached phantom node ("mirror")
           * that serves as the target of Object.defineProperty instead. While we could simply use the subject HTML
           * element instead, this would conflict with element types which use indexed properties (such as forms and
           * select lists).
           */
          if (false === dpSupport) {

            var visage;
            var mirror = addProp.mirror || document.createElement("div");
            var reflections = mirror.childNodes;
            var l = reflections.length;

            for (var i = 0; i < l; ++i)
              if (reflections[i]._R === THIS) {
                visage = reflections[i];
                break;
              }

            /** Couldn't find an element's reflection inside the mirror. Materialise one. */
            visage || (visage = mirror.appendChild(document.createElement("div")));

            tokenList = DOMTokenList.call(visage, THIS, attr);
          } else tokenList = new DOMTokenList(THIS, attr);

          defineGetter(THIS, name, function () {
            return tokenList;
          });
          delete THIS[gibberishProperty];

          return tokenList;
        }, true);
      };

      addProp(global.Element, "classList", "className");
      addProp(global.HTMLElement, "classList", "className");
      addProp(global.HTMLLinkElement, "relList", "rel");
      addProp(global.HTMLAnchorElement, "relList", "rel");
      addProp(global.HTMLAreaElement, "relList", "rel");
    }(this));

}).call('object' === typeof window && window || 'object' === typeof self && self || 'object' === typeof global && global || {});

/**
 * TODO: Ideally this would be a NodeList.prototype.forEach polyfill
 * This seems to fail in IE8, requires more investigation.
 * See: https://github.com/imagitama/nodelist-foreach-polyfill
 */
function nodeListForEach (nodes, callback) {
  if (window.NodeList.prototype.forEach) {
    return nodes.forEach(callback)
  }
  for (var i = 0; i < nodes.length; i++) {
    callback.call(window, nodes[i], i, nodes);
  }
}

function Checkboxes ($module) {
  this.$module = $module;
  this.$inputs = $module.querySelectorAll('input[type="checkbox"]');
}

/**
 * Initialise Checkboxes
 *
 * Checkboxes can be associated with a 'conditionally revealed' content block –
 * for example, a checkbox for 'Phone' could reveal an additional form field for
 * the user to enter their phone number.
 *
 * These associations are made using a `data-aria-controls` attribute, which is
 * promoted to an aria-controls attribute during initialisation.
 *
 * We also need to restore the state of any conditional reveals on the page (for
 * example if the user has navigated back), and set up event handlers to keep
 * the reveal in sync with the checkbox state.
 */
Checkboxes.prototype.init = function () {
  var $module = this.$module;
  var $inputs = this.$inputs;

  nodeListForEach($inputs, function ($input) {
    var target = $input.getAttribute('data-aria-controls');

    // Skip checkboxes without data-aria-controls attributes, or where the
    // target element does not exist.
    if (!target || !document.getElementById(target)) {
      return
    }

    // Promote the data-aria-controls attribute to a aria-controls attribute
    // so that the relationship is exposed in the AOM
    $input.setAttribute('aria-controls', target);
    $input.removeAttribute('data-aria-controls');
  });

  // When the page is restored after navigating 'back' in some browsers the
  // state of form controls is not restored until *after* the DOMContentLoaded
  // event is fired, so we need to sync after the pageshow event in browsers
  // that support it.
  if ('onpageshow' in window) {
    window.addEventListener('pageshow', this.syncAllConditionalReveals.bind(this));
  } else {
    window.addEventListener('DOMContentLoaded', this.syncAllConditionalReveals.bind(this));
  }

  // Although we've set up handlers to sync state on the pageshow or
  // DOMContentLoaded event, init could be called after those events have fired,
  // for example if they are added to the page dynamically, so sync now too.
  this.syncAllConditionalReveals();

  $module.addEventListener('click', this.handleClick.bind(this));
};

/**
 * Sync the conditional reveal states for all inputs in this $module.
 */
Checkboxes.prototype.syncAllConditionalReveals = function () {
  nodeListForEach(this.$inputs, this.syncConditionalRevealWithInputState.bind(this));
};

/**
 * Sync conditional reveal with the input state
 *
 * Synchronise the visibility of the conditional reveal, and its accessible
 * state, with the input's checked state.
 *
 * @param {HTMLInputElement} $input Checkbox input
 */
Checkboxes.prototype.syncConditionalRevealWithInputState = function ($input) {
  var $target = document.getElementById($input.getAttribute('aria-controls'));

  if ($target && $target.classList.contains('govuk-checkboxes__conditional')) {
    var inputIsChecked = $input.checked;

    $input.setAttribute('aria-expanded', inputIsChecked);
    $target.classList.toggle('govuk-checkboxes__conditional--hidden', !inputIsChecked);
  }
};

/**
 * Uncheck other checkboxes
 *
 * Find any other checkbox inputs with the same name value, and uncheck them.
 * This is useful for when a “None of these" checkbox is checked.
 */
Checkboxes.prototype.unCheckAllInputsExcept = function ($input) {
  var allInputsWithSameName = document.querySelectorAll('input[type="checkbox"][name="' + $input.name + '"]');

  nodeListForEach(allInputsWithSameName, function ($inputWithSameName) {
    var hasSameFormOwner = ($input.form === $inputWithSameName.form);
    if (hasSameFormOwner && $inputWithSameName !== $input) {
      $inputWithSameName.checked = false;
      this.syncConditionalRevealWithInputState($inputWithSameName);
    }
  }.bind(this));
};

/**
 * Uncheck exclusive inputs
 *
 * Find any checkbox inputs with the same name value and the 'exclusive' behaviour,
 * and uncheck them. This helps prevent someone checking both a regular checkbox and a
 * "None of these" checkbox in the same fieldset.
 */
Checkboxes.prototype.unCheckExclusiveInputs = function ($input) {
  var allInputsWithSameNameAndExclusiveBehaviour = document.querySelectorAll(
    'input[data-behaviour="exclusive"][type="checkbox"][name="' + $input.name + '"]'
  );

  nodeListForEach(allInputsWithSameNameAndExclusiveBehaviour, function ($exclusiveInput) {
    var hasSameFormOwner = ($input.form === $exclusiveInput.form);
    if (hasSameFormOwner) {
      $exclusiveInput.checked = false;
      this.syncConditionalRevealWithInputState($exclusiveInput);
    }
  }.bind(this));
};

/**
 * Click event handler
 *
 * Handle a click within the $module – if the click occurred on a checkbox, sync
 * the state of any associated conditional reveal with the checkbox state.
 *
 * @param {MouseEvent} event Click event
 */
Checkboxes.prototype.handleClick = function (event) {
  var $target = event.target;

  // Ignore clicks on things that aren't checkbox inputs
  if ($target.type !== 'checkbox') {
    return
  }

  // If the checkbox conditionally-reveals some content, sync the state
  var hasAriaControls = $target.getAttribute('aria-controls');
  if (hasAriaControls) {
    this.syncConditionalRevealWithInputState($target);
  }

  // No further behaviour needed for unchecking
  if (!$target.checked) {
    return
  }

  // Handle 'exclusive' checkbox behaviour (ie "None of these")
  var hasBehaviourExclusive = ($target.getAttribute('data-behaviour') === 'exclusive');
  if (hasBehaviourExclusive) {
    this.unCheckAllInputsExcept($target);
  } else {
    this.unCheckExclusiveInputs($target);
  }
};

return Checkboxes;

})));