// Backbone.Events
  // -----------------

  // A module that can be mixed in to *any object* in order to provide it with
  // custom events. You may `bind` or `unbind` a callback function to an event;
  // `trigger`-ing an event fires all callbacks in succession.
  //
  //     var object = {};
  //     _.extend(object, Backbone.Events);
  //     object.bind('expand', function(){ alert('expanded'); });
  //     object.trigger('expand');
  //
  Backbone.Events = {

    // Bind an event, specified by a string name, `ev`, to a `callback` function.
    // Passing `"all"` will bind the callback to all events fired.
    bind : function(ev, callback, context) {
      var calls = this._callbacks || (this._callbacks = {});
      var list  = calls[ev] || (calls[ev] = {});
      var tail = list.tail || (list.tail = list.next = {});
      tail.callback = callback;
      tail.context = context;
      list.tail = tail.next = {};
      return this;
    },

    // Remove one or many callbacks. If `callback` is null, removes all
    // callbacks for the event. If `ev` is null, removes all bound callbacks
    // for all events.
    unbind : function(ev, callback) {
      var calls, node, prev;
      if (!ev) {
        this._callbacks = null;
      } else if (calls = this._callbacks) {
        if (!callback) {
          calls[ev] = {};
        } else if (node = calls[ev]) {
          while ((prev = node) && (node = node.next)) {
            if (node.callback !== callback) continue;
            prev.next = node.next;
            node.context = node.callback = null;
            break;
          }
        }
      }
      return this;
    },

    // Trigger an event, firing all bound callbacks. Callbacks are passed the
    // same arguments as `trigger` is, apart from the event name.
    // Listening for `"all"` passes the true event name as the first argument.
    trigger : function(eventName) {
      var node, calls, callback, args, ev, events = ['all', eventName];
      if (!(calls = this._callbacks)) return this;
      while (ev = events.pop()) {
        if (!(node = calls[ev])) continue;
        args = ev == 'all' ? arguments : Array.prototype.slice.call(arguments, 1);
        while (node = node.next) if (callback = node.callback) callback.apply(node.context || this, args);
      }
      return this;
    }

  };