text: //     Backbone.js 1.2.0
  
  //     (c) 2010-2015 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
  //     Backbone may be freely distributed under the MIT license.
  //     For all details and documentation:
  //     http://backbonejs.org
  
  (function(factory) {
  
      // Establish the root object, `window` (`self`) in the browser, or `global` on the server.
      // We use `self` instead of `window` for `WebWorker` support.
      var root = (typeof self == 'object' && self.self == self && self) ||
          (typeof global == 'object' && global.global == global && global);
  
      // Set up Backbone appropriately for the environment. Start with AMD.
      if (typeof define === 'function' && define.amd) {
          define(['underscore', 'jquery', 'exports'], function(_, $, exports) {
              // Export global even in AMD case in case this script is loaded with
              // others that may still expect a global Backbone.
              root.Backbone = factory(root, exports, _, $);
          });
  
          // Next for Node.js or CommonJS. jQuery may not be needed as a module.
      } else if (typeof exports !== 'undefined') {
          var _ = require('underscore'), $;
          try { $ = require('jquery'); } catch(e) {}
          factory(root, exports, _, $);
  
          // Finally, as a browser global.
      } else {
          root.Backbone = factory(root, {}, root._, (root.jQuery || root.Zepto || root.ender || root.$));
      }
  
  }(function(root, Backbone, _, $) {
  
      // Initial Setup
      // -------------
  
      // Save the previous value of the `Backbone` variable, so that it can be
      // restored later on, if `noConflict` is used.
      var previousBackbone = root.Backbone;
  
      // Create local references to array methods we'll want to use later.
      var array = [];
      var slice = array.slice;
  
      // Current version of the library. Keep in sync with `package.json`.
      Backbone.VERSION = '1.2.0';
  
      // For Backbone's purposes, jQuery, Zepto, Ender, or My Library (kidding) owns
      // the `$` variable.
      Backbone.$ = $;
  
      // Runs Backbone.js in *noConflict* mode, returning the `Backbone` variable
      // to its previous owner. Returns a reference to this Backbone object.
      Backbone.noConflict = function() {
          root.Backbone = previousBackbone;
          return this;
      };
  
      // Turn on `emulateHTTP` to support legacy HTTP servers. Setting this option
      // will fake `"PATCH"`, `"PUT"` and `"DELETE"` requests via the `_method` parameter and
      // set a `X-Http-Method-Override` header.
      Backbone.emulateHTTP = false;
  
      // Turn on `emulateJSON` to support legacy servers that can't deal with direct
      // `application/json` requests ... this will encode the body as
      // `application/x-www-form-urlencoded` instead and will send the model in a
      // form param named `model`.
      Backbone.emulateJSON = false;
  
      // Backbone.Events
      // ---------------
  
      // A module that can be mixed in to *any object* in order to provide it with
      // custom events. You may bind with `on` or remove with `off` callback
      // functions to an event; `trigger`-ing an event fires all callbacks in
      // succession.
      //
      //     var object = {};
      //     _.extend(object, Backbone.Events);
      //     object.on('expand', function(){ alert('expanded'); });
      //     object.trigger('expand');
      //
      var Events = Backbone.Events = {};
  
      // Regular expression used to split event strings.
      var eventSplitter = /\s+/;
  
      // Iterates over the standard `event, callback` (as well as the fancy multiple
      // space-separated events `"change blur", callback` and jQuery-style event
      // maps `{event: callback}`), reducing them by manipulating `memo`.
      // Passes a normalized single event name and callback, as well as any
      // optional `opts`.
      var eventsApi = function(iteratee, memo, name, callback, opts) {
          var i = 0, names;
          if (name && typeof name === 'object') {
              // Handle event maps.
              for (names = _.keys(name); i < names.length ; i++) {
                  memo = iteratee(memo, names[i], name[names[i]], opts);
              }
          } else if (name && eventSplitter.test(name)) {
              // Handle space separated event names.
              for (names = name.split(eventSplitter); i < names.length; i++) {
                  memo = iteratee(memo, names[i], callback, opts);
              }
          } else {
              memo = iteratee(memo, name, callback, opts);
          }
          return memo;
      };
  
      // Bind an event to a `callback` function. Passing `"all"` will bind
      // the callback to all events fired.
      Events.on = function(name, callback, context) {
          return internalOn(this, name, callback, context);
      };
  
      // An internal use `on` function, used to guard the `listening` argument from
      // the public API.
      var internalOn = function(obj, name, callback, context, listening) {
          obj._events = eventsApi(onApi, obj._events || {}, name, callback, {
              context: context,
              ctx: obj,
              listening: listening
          });
  
          if (listening) {
              var listeners = obj._listeners || (obj._listeners = {});
              listeners[listening.id] = listening;
          }
  
          return obj;
      };
  
      // Inversion-of-control versions of `on`. Tell *this* object to listen to
      // an event in another object... keeping track of what it's listening to.
      Events.listenTo =  function(obj, name, callback) {
          if (!obj) return this;
          var id = obj._listenId || (obj._listenId = _.uniqueId('l'));
          var listeningTo = this._listeningTo || (this._listeningTo = {});
          var listening = listeningTo[id];
  
          // This object is not listening to any other events on `obj` yet.
          // Setup the necessary references to track the listening callbacks.
          if (!listening) {
              var thisId = this._listenId || (this._listenId = _.uniqueId('l'));
              listening = listeningTo[id] = {obj: obj, objId: id, id: thisId, listeningTo: listeningTo, count: 0};
          }
  
          // Bind callbacks on obj, and keep track of them on listening.
          internalOn(obj, name, callback, this, listening);
          return this;
      };
  
      // The reducing API that adds a callback to the `events` object.
      var onApi = function(events, name, callback, options) {
          if (callback) {
              var handlers = events[name] || (events[name] = []);
              var context = options.context, ctx = options.ctx, listening = options.listening;
              if (listening) listening.count++;
  
              handlers.push({ callback: callback, context: context, ctx: context || ctx, listening: listening });
          }
          return events;
      };
  
      // Remove one or many callbacks. If `context` is null, removes all
      // callbacks with that function. If `callback` is null, removes all
      // callbacks for the event. If `name` is null, removes all bound
      // callbacks for all events.
      Events.off =  function(name, callback, context) {
          if (!this._events) return this;
          this._events = eventsApi(offApi, this._events, name, callback, {
              context: context,
              listeners: this._listeners
          });
          return this;
      };
  
      // Tell this object to stop listening to either specific events ... or
      // to every object it's currently listening to.
      Events.stopListening =  function(obj, name, callback) {
          var listeningTo = this._listeningTo;
          if (!listeningTo) return this;
  
          var ids = obj ? [obj._listenId] : _.keys(listeningTo);
  
          for (var i = 0; i < ids.length; i++) {
              var listening = listeningTo[ids[i]];
  
              // If listening doesn't exist, this object is not currently
              // listening to obj. Break out early.
              if (!listening) break;
  
              listening.obj.off(name, callback, this);
          }
          if (_.isEmpty(listeningTo)) this._listeningTo = void 0;
  
          return this;
      };
  
      // The reducing API that removes a callback from the `events` object.
      var offApi = function(events, name, callback, options) {
          // No events to consider.
          if (!events) return;
  
          var i = 0, length, listening;
          var context = options.context, listeners = options.listeners;
  
          // Delete all events listeners and "drop" events.
          if (!name && !callback && !context) {
              var ids = _.keys(listeners);
              for (; i < ids.length; i++) {
                  listening = listeners[ids[i]];
                  delete listeners[listening.id];
                  delete listening.listeningTo[listening.objId];
              }
              return;
          }
  
          var names = name ? [name] : _.keys(events);
          for (; i < names.length; i++) {
              name = names[i];
              var handlers = events[name];
  
              // Bail out if there are no events stored.
              if (!handlers) break;
  
              // Replace events if there are any remaining.  Otherwise, clean up.
              var remaining = [];
              for (var j = 0; j < handlers.length; j++) {
                  var handler = handlers[j];
                  if (
                      callback && callback !== handler.callback &&
                      callback !== handler.callback._callback ||
                      context && context !== handler.context
                  ) {
                      remaining.push(handler);
                  } else {
                      listening = handler.listening;
                      if (listening && --listening.count === 0) {
                          delete listeners[listening.id];
                          delete listening.listeningTo[listening.objId];
                      }
                  }
              }
  
              // Update tail event if the list has any events.  Otherwise, clean up.
              if (remaining.length) {
                  events[name] = remaining;
              } else {
                  delete events[name];
              }
          }
          if (_.size(events)) return events;
      };
  
      // Bind an event to only be triggered a single time. After the first time
      // the callback is invoked, it will be removed. When multiple events are
      // passed in using the space-separated syntax, the event will fire once for every
      // event you passed in, not once for a combination of all events
      Events.once =  function(name, callback, context) {
          // Map the event into a `{event: once}` object.
          var events = eventsApi(onceMap, {}, name, callback, _.bind(this.off, this));
          return this.on(events, void 0, context);
      };
  
      // Inversion-of-control versions of `once`.
      Events.listenToOnce =  function(obj, name, callback) {
          // Map the event into a `{event: once}` object.
          var events = eventsApi(onceMap, {}, name, callback, _.bind(this.stopListening, this, obj));
          return this.listenTo(obj, events);
      };
  
      // Reduces the event callbacks into a map of `{event: onceWrapper}`.
      // `offer` unbinds the `onceWrapper` after it as been called.
      var onceMap = function(map, name, callback, offer) {
          if (callback) {
              var once = map[name] = _.once(function() {
                  offer(name, once);
                  callback.apply(this, arguments);
              });
              once._callback = callback;
          }
          return map;
      };
  
      // Trigger one or many events, firing all bound callbacks. Callbacks are
      // passed the same arguments as `trigger` is, apart from the event name
      // (unless you're listening on `"all"`, which will cause your callback to
      // receive the true name of the event as the first argument).
      Events.trigger =  function(name) {
          if (!this._events) return this;
  
          var length = Math.max(0, arguments.length - 1);
          var args = Array(length);
          for (var i = 0; i < length; i++) args[i] = arguments[i + 1];
  
          eventsApi(triggerApi, this._events, name, void 0, args);
          return this;
      };
  
      // Handles triggering the appropriate event callbacks.
      var triggerApi = function(objEvents, name, cb, args) {
          if (objEvents) {
              var events = objEvents[name];
              var allEvents = objEvents.all;
              if (events && allEvents) allEvents = allEvents.slice();
              if (events) triggerEvents(events, args);
              if (allEvents) triggerEvents(allEvents, [name].concat(args));
          }
          return objEvents;
      };
  
      // A difficult-to-believe, but optimized internal dispatch function for
      // triggering events. Tries to keep the usual cases speedy (most internal
      // Backbone events have 3 arguments).
      var triggerEvents = function(events, args) {
          var ev, i = -1, l = events.length, a1 = args[0], a2 = args[1], a3 = args[2];
          switch (args.length) {
              case 0: while (++i < l) (ev = events[i]).callback.call(ev.ctx); return;
              case 1: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1); return;
              case 2: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2); return;
              case 3: while (++i < l) (ev = events[i]).callback.call(ev.ctx, a1, a2, a3); return;
              default: while (++i < l) (ev = events[i]).callback.apply(ev.ctx, args); return;
          }
      };
  
      // Proxy Underscore methods to a Backbone class' prototype using a
      // particular attribute as the data argument
      var addMethod = function(length, method, attribute) {
          switch (length) {
              case 1: return function() {
                  return _[method](this[attribute]);
              };
              case 2: return function(value) {
                  return _[method](this[attribute], value);
              };
              case 3: return function(iteratee, context) {
                  return _[method](this[attribute], iteratee, context);
              };
              case 4: return function(iteratee, defaultVal, context) {
                  return _[method](this[attribute], iteratee, defaultVal, context);
              };
              default: return function() {
                  var args = slice.call(arguments);
                  args.unshift(this[attribute]);
                  return _[method].apply(_, args);
              };
          }
      };
      var addUnderscoreMethods = function(Class, methods, attribute) {
          _.each(methods, function(length, method) {
              if (_[method]) Class.prototype[method] = addMethod(length, method, attribute);
          });
      };
  
      // Aliases for backwards compatibility.
      Events.bind   = Events.on;
      Events.unbind = Events.off;
  
      // Allow the `Backbone` object to serve as a global event bus, for folks who
      // want global "pubsub" in a convenient place.
      _.extend(Backbone, Events);
  
      // Backbone.Model
      // --------------
  
      // Backbone **Models** are the basic data object in the framework --
      // frequently representing a row in a table in a database on your server.
      // A discrete chunk of data and a bunch of useful, related methods for
      // performing computations and transformations on that data.
  
      // Create a new model with the specified attributes. A client id (`cid`)
      // is automatically generated and assigned for you.
      var Model = Backbone.Model = function(attributes, options) {
          var attrs = attributes || {};
          options || (options = {});
          this.cid = _.uniqueId(this.cidPrefix);
          this.attributes = {};
          if (options.collection) this.collection = options.collection;
          if (options.parse) attrs = this.parse(attrs, options) || {};
          attrs = _.defaults({}, attrs, _.result(this, 'defaults'));
          this.set(attrs, options);
          this.changed = {};
          this.initialize.apply(this, arguments);
      };
  
      // Attach all inheritable methods to the Model prototype.
      _.extend(Model.prototype, Events, {
  
          // A hash of attributes whose current and previous value differ.
          changed: null,
  
          // The value returned during the last failed validation.
          validationError: null,
  
          // The default name for the JSON `id` attribute is `"id"`. MongoDB and
          // CouchDB users may want to set this to `"_id"`.
          idAttribute: 'id',
  
          // The prefix is used to create the client id which is used to identify models locally.
          // You may want to override this if you're experiencing name clashes with model ids.
          cidPrefix: 'c',
  
          // Initialize is an empty function by default. Override it with your own
          // initialization logic.
          initialize: function(){},
  
          // Return a copy of the model's `attributes` object.
          toJSON: function(options) {
              return _.clone(this.attributes);
          },
  
          // Proxy `Backbone.sync` by default -- but override this if you need
          // custom syncing semantics for *this* particular model.
          sync: function() {
              return Backbone.sync.apply(this, arguments);
          },
  
          // Get the value of an attribute.
          get: function(attr) {
              return this.attributes[attr];
          },
  
          // Get the HTML-escaped value of an attribute.
          escape: function(attr) {
              return _.escape(this.get(attr));
          },
  
          // Returns `true` if the attribute contains a value that is not null
          // or undefined.
          has: function(attr) {
              return this.get(attr) != null;
          },
  
          // Special-cased proxy to underscore's `_.matches` method.
          matches: function(attrs) {
              return !!_.iteratee(attrs, this)(this.attributes);
          },
  
          // Set a hash of model attributes on the object, firing `"change"`. This is
          // the core primitive operation of a model, updating the data and notifying
          // anyone who needs to know about the change in state. The heart of the beast.
          set: function(key, val, options) {
              var attr, attrs, unset, changes, silent, changing, prev, current;
              if (key == null) return this;
  
              // Handle both `"key", value` and `{key: value}` -style arguments.
              if (typeof key === 'object') {
                  attrs = key;
                  options = val;
              } else {
                  (attrs = {})[key] = val;
              }
  
              options || (options = {});
  
              // Run validation.
              if (!this._validate(attrs, options)) return false;
  
              // Extract attributes and options.
              unset           = options.unset;
              silent          = options.silent;
              changes         = [];
              changing        = this._changing;
              this._changing  = true;
  
              if (!changing) {
                  this._previousAttributes = _.clone(this.attributes);
                  this.changed = {};
              }
              current = this.attributes, prev = this._previousAttributes;
  
              // Check for changes of `id`.
              if (this.idAttribute in attrs) this.id = attrs[this.idAttribute];
  
              // For each `set` attribute, update or delete the current value.
              for (attr in attrs) {
                  val = attrs[attr];
                  if (!_.isEqual(current[attr], val)) changes.push(attr);
                  if (!_.isEqual(prev[attr], val)) {
                      this.changed[attr] = val;
                  } else {
                      delete this.changed[attr];
                  }
                  unset ? delete current[attr] : current[attr] = val;
              }
  
              // Trigger all relevant attribute changes.
              if (!silent) {
                  if (changes.length) this._pending = options;
                  for (var i = 0; i < changes.length; i++) {
                      this.trigger('change:' + changes[i], this, current[changes[i]], options);
                  }
              }
  
              // You might be wondering why there's a `while` loop here. Changes can
              // be recursively nested within `"change"` events.
              if (changing) return this;
              if (!silent) {
                  while (this._pending) {
                      options = this._pending;
                      this._pending = false;
                      this.trigger('change', this, options);
                  }
              }
              this._pending = false;
              this._changing = false;
              return this;
          },
  
          // Remove an attribute from the model, firing `"change"`. `unset` is a noop
          // if the attribute doesn't exist.
          unset: function(attr, options) {
              return this.set(attr, void 0, _.extend({}, options, {unset: true}));
          },
  
          // Clear all attributes on the model, firing `"change"`.
          clear: function(options) {
              var attrs = {};
              for (var key in this.attributes) attrs[key] = void 0;
              return this.set(attrs, _.extend({}, options, {unset: true}));
          },
  
          // Determine if the model has changed since the last `"change"` event.
          // If you specify an attribute name, determine if that attribute has changed.
          hasChanged: function(attr) {
              if (attr == null) return !_.isEmpty(this.changed);
              return _.has(this.changed, attr);
          },
  
          // Return an object containing all the attributes that have changed, or
          // false if there are no changed attributes. Useful for determining what
          // parts of a view need to be updated and/or what attributes need to be
          // persisted to the server. Unset attributes will be set to undefined.
          // You can also pass an attributes object to diff against the model,
          // determining if there *would be* a change.
          changedAttributes: function(diff) {
              if (!diff) return this.hasChanged() ? _.clone(this.changed) : false;
              var val, changed = false;
              var old = this._changing ? this._previousAttributes : this.attributes;
              for (var attr in diff) {
                  if (_.isEqual(old[attr], (val = diff[attr]))) continue;
                  (changed || (changed = {}))[attr] = val;
              }
              return changed;
          },
  
          // Get the previous value of an attribute, recorded at the time the last
          // `"change"` event was fired.
          previous: function(attr) {
              if (attr == null || !this._previousAttributes) return null;
              return this._previousAttributes[attr];
          },
  
          // Get all of the attributes of the model at the time of the previous
          // `"change"` event.
          previousAttributes: function() {
              return _.clone(this._previousAttributes);
          },
  
          // Fetch the model from the server, merging the response with the model's
          // local attributes. Any changed attributes will trigger a "change" event.
          fetch: function(options) {
              options = options ? _.clone(options) : {};
              if (options.parse === void 0) options.parse = true;
              var model = this;
              var success = options.success;
              options.success = function(resp) {
                  if (!model.set(model.parse(resp, options), options)) return false;
                  if (success) success.call(options.context, model, resp, options);
                  model.trigger('sync', model, resp, options);
              };
              wrapError(this, options);
              return this.sync('read', this, options);
          },
  
          // Set a hash of model attributes, and sync the model to the server.
          // If the server returns an attributes hash that differs, the model's
          // state will be `set` again.
          save: function(key, val, options) {
              var attrs, method, xhr, attributes = this.attributes, wait;
  
              // Handle both `"key", value` and `{key: value}` -style arguments.
              if (key == null || typeof key === 'object') {
                  attrs = key;
                  options = val;
              } else {
                  (attrs = {})[key] = val;
              }
  
              options = _.extend({validate: true}, options);
              wait = options.wait;
  
              // If we're not waiting and attributes exist, save acts as
              // `set(attr).save(null, opts)` with validation. Otherwise, check if
              // the model will be valid when the attributes, if any, are set.
              if (attrs && !wait) {
                  if (!this.set(attrs, options)) return false;
              } else {
                  if (!this._validate(attrs, options)) return false;
              }
  
              // Set temporary attributes if `{wait: true}`.
              if (attrs && wait) {
                  this.attributes = _.extend({}, attributes, attrs);
              }
  
              // After a successful server-side save, the client is (optionally)
              // updated with the server-side state.
              if (options.parse === void 0) options.parse = true;
              var model = this;
              var success = options.success;
              options.success = function(resp) {
                  // Ensure attributes are restored during synchronous saves.
                  model.attributes = attributes;
                  var serverAttrs = options.parse ? model.parse(resp, options) : resp;
                  if (wait) serverAttrs = _.extend(attrs || {}, serverAttrs);
                  if (_.isObject(serverAttrs) && !model.set(serverAttrs, options)) {
                      return false;
                  }
                  if (success) success.call(options.context, model, resp, options);
                  model.trigger('sync', model, resp, options);
              };
              wrapError(this, options);
  
              method = this.isNew() ? 'create' : (options.patch ? 'patch' : 'update');
              if (method === 'patch' && !options.attrs) options.attrs = attrs;
              xhr = this.sync(method, this, options);
  
              // Restore attributes.
              if (attrs && wait) this.attributes = attributes;
  
              return xhr;
          },
  
          // Destroy this model on the server if it was already persisted.
          // Optimistically removes the model from its collection, if it has one.
          // If `wait: true` is passed, waits for the server to respond before removal.
          destroy: function(options) {
              options = options ? _.clone(options) : {};
              var model = this;
              var success = options.success;
              var wait = options.wait;
  
              var destroy = function() {
                  model.stopListening();
                  model.trigger('destroy', model, model.collection, options);
              };
  
              options.success = function(resp) {
                  if (wait) destroy();
                  if (success) success.call(options.context, model, resp, options);
                  if (!model.isNew()) model.trigger('sync', model, resp, options);
              };
  
              var xhr = false;
              if (this.isNew()) {
                  _.defer(options.success);
              } else {
                  wrapError(this, options);
                  xhr = this.sync('delete', this, options);
              }
              if (!wait) destroy();
              return xhr;
          },
  
          // Default URL for the model's representation on the server -- if you're
          // using Backbone's restful methods, override this to change the endpoint
          // that will be called.
          url: function() {
              var base =
                  _.result(this, 'urlRoot') ||
                  _.result(this.collection, 'url') ||
                  urlError();
              if (this.isNew()) return base;
              var id = this.id || this.attributes[this.idAttribute];
              return base.replace(/([^\/])$/, '$1/') + encodeURIComponent(id);
          },
  
          // **parse** converts a response into the hash of attributes to be `set` on
          // the model. The default implementation is just to pass the response along.
          parse: function(resp, options) {
              return resp;
          },
  
          // Create a new model with identical attributes to this one.
          clone: function() {
              return new this.constructor(this.attributes);
          },
  
          // A model is new if it has never been saved to the server, and lacks an id.
          isNew: function() {
              return !this.has(this.idAttribute);
          },
  
          // Check if the model is currently in a valid state.
          isValid: function(options) {
              return this._validate({}, _.extend(options || {}, { validate: true }));
          },
  
          // Run validation against the next complete set of model attributes,
          // returning `true` if all is well. Otherwise, fire an `"invalid"` event.
          _validate: function(attrs, options) {
              if (!options.validate || !this.validate) return true;
              attrs = _.extend({}, this.attributes, attrs);
              var error = this.validationError = this.validate(attrs, options) || null;
              if (!error) return true;
              this.trigger('invalid', this, error, _.extend(options, {validationError: error}));
              return false;
          }
  
      });
  
      // Underscore methods that we want to implement on the Model.
      var modelMethods = { keys: 1, values: 1, pairs: 1, invert: 1, pick: 0,
          omit: 0, chain: 1, isEmpty: 1 };
  
      // Mix in each Underscore method as a proxy to `Model#attributes`.
      addUnderscoreMethods(Model, modelMethods, 'attributes');
  
      // Backbone.Collection
      // -------------------
  
      // If models tend to represent a single row of data, a Backbone Collection is
      // more analogous to a table full of data ... or a small slice or page of that
      // table, or a collection of rows that belong together for a particular reason
      // -- all of the messages in this particular folder, all of the documents
      // belonging to this particular author, and so on. Collections maintain
      // indexes of their models, both in order, and for lookup by `id`.
  
      // Create a new **Collection**, perhaps to contain a specific type of `model`.
      // If a `comparator` is specified, the Collection will maintain
      // its models in sort order, as they're added and removed.
      var Collection = Backbone.Collection = function(models, options) {
          options || (options = {});
          if (options.model) this.model = options.model;
          if (options.comparator !== void 0) this.comparator = options.comparator;
          this._reset();
          this.initialize.apply(this, arguments);
          if (models) this.reset(models, _.extend({silent: true}, options));
      };
  
      // Default options for `Collection#set`.
      var setOptions = {add: true, remove: true, merge: true};
      var addOptions = {add: true, remove: false};
  
      // Define the Collection's inheritable methods.
      _.extend(Collection.prototype, Events, {
  
          // The default model for a collection is just a **Backbone.Model**.
          // This should be overridden in most cases.
          model: Model,
  
          // Initialize is an empty function by default. Override it with your own
          // initialization logic.
          initialize: function(){},
  
          // The JSON representation of a Collection is an array of the
          // models' attributes.
          toJSON: function(options) {
              return this.map(function(model){ return model.toJSON(options); });
          },
  
          // Proxy `Backbone.sync` by default.
          sync: function() {
              return Backbone.sync.apply(this, arguments);
          },
  
          // Add a model, or list of models to the set.
          add: function(models, options) {
              return this.set(models, _.extend({merge: false}, options, addOptions));
          },
  
          // Remove a model, or a list of models from the set.
          remove: function(models, options) {
              var singular = !_.isArray(models), removed;
              models = singular ? [models] : _.clone(models);
              options || (options = {});
              removed = this._removeModels(models, options);
              if (!options.silent && removed) this.trigger('update', this, options);
              return singular ? models[0] : models;
          },
  
          // Update a collection by `set`-ing a new list of models, adding new ones,
          // removing models that are no longer present, and merging models that
          // already exist in the collection, as necessary. Similar to **Model#set**,
          // the core operation for updating the data contained by the collection.
          set: function(models, options) {
              options = _.defaults({}, options, setOptions);
              if (options.parse) models = this.parse(models, options);
              var singular = !_.isArray(models);
              models = singular ? (models ? [models] : []) : models.slice();
              var id, model, attrs, existing, sort;
              var at = options.at;
              if (at != null) at = +at;
              if (at < 0) at += this.length + 1;
              var sortable = this.comparator && (at == null) && options.sort !== false;
              var sortAttr = _.isString(this.comparator) ? this.comparator : null;
              var toAdd = [], toRemove = [], modelMap = {};
              var add = options.add, merge = options.merge, remove = options.remove;
              var order = !sortable && add && remove ? [] : false;
              var orderChanged = false;
  
              // Turn bare objects into model references, and prevent invalid models
              // from being added.
              for (var i = 0; i < models.length; i++) {
                  attrs = models[i];
  
                  // If a duplicate is found, prevent it from being added and
                  // optionally merge it into the existing model.
                  if (existing = this.get(attrs)) {
                      if (remove) modelMap[existing.cid] = true;
                      if (merge && attrs !== existing) {
                          attrs = this._isModel(attrs) ? attrs.attributes : attrs;
                          if (options.parse) attrs = existing.parse(attrs, options);
                          existing.set(attrs, options);
                          if (sortable && !sort && existing.hasChanged(sortAttr)) sort = true;
                      }
                      models[i] = existing;
  
                      // If this is a new, valid model, push it to the `toAdd` list.
                  } else if (add) {
                      model = models[i] = this._prepareModel(attrs, options);
                      if (!model) continue;
                      toAdd.push(model);
                      this._addReference(model, options);
                  }
  
                  // Do not add multiple models with the same `id`.
                  model = existing || model;
                  if (!model) continue;
                  id = this.modelId(model.attributes);
                  if (order && (model.isNew() || !modelMap[id])) {
                      order.push(model);
  
                      // Check to see if this is actually a new model at this index.
                      orderChanged = orderChanged || !this.models[i] || model.cid !== this.models[i].cid;
                  }
  
                  modelMap[id] = true;
              }
  
              // Remove nonexistent models if appropriate.
              if (remove) {
                  for (var i = 0; i < this.length; i++) {
                      if (!modelMap[(model = this.models[i]).cid]) toRemove.push(model);
                  }
                  if (toRemove.length) this._removeModels(toRemove, options);
              }
  
              // See if sorting is needed, update `length` and splice in new models.
              if (toAdd.length || orderChanged) {
                  if (sortable) sort = true;
                  this.length += toAdd.length;
                  if (at != null) {
                      for (var i = 0; i < toAdd.length; i++) {
                          this.models.splice(at + i, 0, toAdd[i]);
                      }
                  } else {
                      if (order) this.models.length = 0;
                      var orderedModels = order || toAdd;
                      for (var i = 0; i < orderedModels.length; i++) {
                          this.models.push(orderedModels[i]);
                      }
                  }
              }
  
              // Silently sort the collection if appropriate.
              if (sort) this.sort({silent: true});
  
              // Unless silenced, it's time to fire all appropriate add/sort events.
              if (!options.silent) {
                  var addOpts = at != null ? _.clone(options) : options;
                  for (var i = 0; i < toAdd.length; i++) {
                      if (at != null) addOpts.index = at + i;
                      (model = toAdd[i]).trigger('add', model, this, addOpts);
                  }
                  if (sort || orderChanged) this.trigger('sort', this, options);
                  if (toAdd.length || toRemove.length) this.trigger('update', this, options);
              }
  
              // Return the added (or merged) model (or models).
              return singular ? models[0] : models;
          },
  
          // When you have more items than you want to add or remove individually,
          // you can reset the entire set with a new list of models, without firing
          // any granular `add` or `remove` events. Fires `reset` when finished.
          // Useful for bulk operations and optimizations.
          reset: function(models, options) {
              options = options ? _.clone(options) : {};
              for (var i = 0; i < this.models.length; i++) {
                  this._removeReference(this.models[i], options);
              }
              options.previousModels = this.models;
              this._reset();
              models = this.add(models, _.extend({silent: true}, options));
              if (!options.silent) this.trigger('reset', this, options);
              return models;
          },
  
          // Add a model to the end of the collection.
          push: function(model, options) {
              return this.add(model, _.extend({at: this.length}, options));
          },
  
          // Remove a model from the end of the collection.
          pop: function(options) {
              var model = this.at(this.length - 1);
              this.remove(model, options);
              return model;
          },
  
          // Add a model to the beginning of the collection.
          unshift: function(model, options) {
              return this.add(model, _.extend({at: 0}, options));
          },
  
          // Remove a model from the beginning of the collection.
          shift: function(options) {
              var model = this.at(0);
              this.remove(model, options);
              return model;
          },
  
          // Slice out a sub-array of models from the collection.
          slice: function() {
              return slice.apply(this.models, arguments);
          },
  
          // Get a model from the set by id.
          get: function(obj) {
              if (obj == null) return void 0;
              var id = this.modelId(this._isModel(obj) ? obj.attributes : obj);
              return this._byId[obj] || this._byId[id] || this._byId[obj.cid];
          },
  
          // Get the model at the given index.
          at: function(index) {
              if (index < 0) index += this.length;
              return this.models[index];
          },
  
          // Return models with matching attributes. Useful for simple cases of
          // `filter`.
          where: function(attrs, first) {
              var matches = _.matches(attrs);
              return this[first ? 'find' : 'filter'](function(model) {
                  return matches(model.attributes);
              });
          },
  
          // Return the first model with matching attributes. Useful for simple cases
          // of `find`.
          findWhere: function(attrs) {
              return this.where(attrs, true);
          },
  
          // Force the collection to re-sort itself. You don't need to call this under
          // normal circumstances, as the set will maintain sort order as each item
          // is added.
          sort: function(options) {
              if (!this.comparator) throw new Error('Cannot sort a set without a comparator');
              options || (options = {});
  
              // Run sort based on type of `comparator`.
              if (_.isString(this.comparator) || this.comparator.length === 1) {
                  this.models = this.sortBy(this.comparator, this);
              } else {
                  this.models.sort(_.bind(this.comparator, this));
              }
  
              if (!options.silent) this.trigger('sort', this, options);
              return this;
          },
  
          // Pluck an attribute from each model in the collection.
          pluck: function(attr) {
              return _.invoke(this.models, 'get', attr);
          },
  
          // Fetch the default set of models for this collection, resetting the
          // collection when they arrive. If `reset: true` is passed, the response
          // data will be passed through the `reset` method instead of `set`.
          fetch: function(options) {
              options = options ? _.clone(options) : {};
              if (options.parse === void 0) options.parse = true;
              var success = options.success;
              var collection = this;
              options.success = function(resp) {
                  var method = options.reset ? 'reset' : 'set';
                  collection[method](resp, options);
                  if (success) success.call(options.context, collection, resp, options);
                  collection.trigger('sync', collection, resp, options);
              };
              wrapError(this, options);
              return this.sync('read', this, options);
          },
  
          // Create a new instance of a model in this collection. Add the model to the
          // collection immediately, unless `wait: true` is passed, in which case we
          // wait for the server to agree.
          create: function(model, options) {
              options = options ? _.clone(options) : {};
              var wait = options.wait;
              if (!(model = this._prepareModel(model, options))) return false;
              if (!wait) this.add(model, options);
              var collection = this;
              var success = options.success;
              options.success = function(model, resp, callbackOpts) {
                  if (wait) collection.add(model, callbackOpts);
                  if (success) success.call(callbackOpts.context, model, resp, callbackOpts);
              };
              model.save(null, options);
              return model;
          },
  
          // **parse** converts a response into a list of models to be added to the
          // collection. The default implementation is just to pass it through.
          parse: function(resp, options) {
              return resp;
          },
  
          // Create a new collection with an identical list of models as this one.
          clone: function() {
              return new this.constructor(this.models, {
                  model: this.model,
                  comparator: this.comparator
              });
          },
  
          // Define how to uniquely identify models in the collection.
          modelId: function (attrs) {
              return attrs[this.model.prototype.idAttribute || 'id'];
          },
  
          // Private method to reset all internal state. Called when the collection
          // is first initialized or reset.
          _reset: function() {
              this.length = 0;
              this.models = [];
              this._byId  = {};
          },
  
          // Prepare a hash of attributes (or other model) to be added to this
          // collection.
          _prepareModel: function(attrs, options) {
              if (this._isModel(attrs)) {
                  if (!attrs.collection) attrs.collection = this;
                  return attrs;
              }
              options = options ? _.clone(options) : {};
              options.collection = this;
              var model = new this.model(attrs, options);
              if (!model.validationError) return model;
              this.trigger('invalid', this, model.validationError, options);
              return false;
          },
  
          // Internal method called by both remove and set. Does not trigger any
          // additional events. Returns true if anything was actually removed.
          _removeModels: function(models, options) {
              var i, l, index, model, removed = false;
              for (var i = 0, j = 0; i < models.length; i++) {
                  var model = models[i] = this.get(models[i]);
                  if (!model) continue;
                  var id = this.modelId(model.attributes);
                  if (id != null) delete this._byId[id];
                  delete this._byId[model.cid];
                  var index = this.indexOf(model);
                  this.models.splice(index, 1);
                  this.length--;
                  if (!options.silent) {
                      options.index = index;
                      model.trigger('remove', model, this, options);
                  }
                  models[j++] = model;
                  this._removeReference(model, options);
                  removed = true;
              }
              // We only need to slice if models array should be smaller, which is
              // caused by some models not actually getting removed.
              if (models.length !== j) models = models.slice(0, j);
              return removed;
          },
  
          // Method for checking whether an object should be considered a model for
          // the purposes of adding to the collection.
          _isModel: function (model) {
              return model instanceof Model;
          },
  
          // Internal method to create a model's ties to a collection.
          _addReference: function(model, options) {
              this._byId[model.cid] = model;
              var id = this.modelId(model.attributes);
              if (id != null) this._byId[id] = model;
              model.on('all', this._onModelEvent, this);
          },
  
          // Internal method to sever a model's ties to a collection.
          _removeReference: function(model, options) {
              if (this === model.collection) delete model.collection;
              model.off('all', this._onModelEvent, this);
          },
  
          // Internal method called every time a model in the set fires an event.
          // Sets need to update their indexes when models change ids. All other
          // events simply proxy through. "add" and "remove" events that originate
          // in other collections are ignored.
          _onModelEvent: function(event, model, collection, options) {
              if ((event === 'add' || event === 'remove') && collection !== this) return;
              if (event === 'destroy') this.remove(model, options);
              if (event === 'change') {
                  var prevId = this.modelId(model.previousAttributes());
                  var id = this.modelId(model.attributes);
                  if (prevId !== id) {
                      if (prevId != null) delete this._byId[prevId];
                      if (id != null) this._byId[id] = model;
                  }
              }
              this.trigger.apply(this, arguments);
          }
  
      });
  
      // Underscore methods that we want to implement on the Collection.
      // 90% of the core usefulness of Backbone Collections is actually implemented
      // right here:
      var collectionMethods = { forEach: 3, each: 3, map: 3, collect: 3, reduce: 4,
          foldl: 4, inject: 4, reduceRight: 4, foldr: 4, find: 3, detect: 3, filter: 3,
          select: 3, reject: 3, every: 3, all: 3, some: 3, any: 3, include: 2,
          contains: 2, invoke: 2, max: 3, min: 3, toArray: 1, size: 1, first: 3,
          head: 3, take: 3, initial: 3, rest: 3, tail: 3, drop: 3, last: 3,
          without: 0, difference: 0, indexOf: 3, shuffle: 1, lastIndexOf: 3,
          isEmpty: 1, chain: 1, sample: 3, partition: 3 };
  
      // Mix in each Underscore method as a proxy to `Collection#models`.
      addUnderscoreMethods(Collection, collectionMethods, 'models');
  
      // Underscore methods that take a property name as an argument.
      var attributeMethods = ['groupBy', 'countBy', 'sortBy', 'indexBy'];
  
      // Use attributes instead of properties.
      _.each(attributeMethods, function(method) {
          if (!_[method]) return;
          Collection.prototype[method] = function(value, context) {
              var iterator = _.isFunction(value) ? value : function(model) {
                  return model.get(value);
              };
              return _[method](this.models, iterator, context);
          };
      });
  
      // Backbone.View
      // -------------
  
      // Backbone Views are almost more convention than they are actual code. A View
      // is simply a JavaScript object that represents a logical chunk of UI in the
      // DOM. This might be a single item, an entire list, a sidebar or panel, or
      // even the surrounding frame which wraps your whole app. Defining a chunk of
      // UI as a **View** allows you to define your DOM events declaratively, without
      // having to worry about render order ... and makes it easy for the view to
      // react to specific changes in the state of your models.
  
      // Creating a Backbone.View creates its initial element outside of the DOM,
      // if an existing element is not provided...
      var View = Backbone.View = function(options) {
          this.cid = _.uniqueId('view');
          options || (options = {});
          _.extend(this, _.pick(options, viewOptions));
          this._ensureElement();
          this.initialize.apply(this, arguments);
      };
  
      // Cached regex to split keys for `delegate`.
      var delegateEventSplitter = /^(\S+)\s*(.*)$/;
  
      // List of view options to be merged as properties.
      var viewOptions = ['model', 'collection', 'el', 'id', 'attributes', 'className', 'tagName', 'events'];
  
      // Set up all inheritable **Backbone.View** properties and methods.
      _.extend(View.prototype, Events, {
  
          // The default `tagName` of a View's element is `"div"`.
          tagName: 'div',
  
          // jQuery delegate for element lookup, scoped to DOM elements within the
          // current view. This should be preferred to global lookups where possible.
          $: function(selector) {
              return this.$el.find(selector);
          },
  
          // Initialize is an empty function by default. Override it with your own
          // initialization logic.
          initialize: function(){},
  
          // **render** is the core function that your view should override, in order
          // to populate its element (`this.el`), with the appropriate HTML. The
          // convention is for **render** to always return `this`.
          render: function() {
              return this;
          },
  
          // Remove this view by taking the element out of the DOM, and removing any
          // applicable Backbone.Events listeners.
          remove: function() {
              this._removeElement();
              this.stopListening();
              return this;
          },
  
          // Remove this view's element from the document and all event listeners
          // attached to it. Exposed for subclasses using an alternative DOM
          // manipulation API.
          _removeElement: function() {
              this.$el.remove();
          },
  
          // Change the view's element (`this.el` property) and re-delegate the
          // view's events on the new element.
          setElement: function(element) {
              this.undelegateEvents();
              this._setElement(element);
              this.delegateEvents();
              return this;
          },
  
          // Creates the `this.el` and `this.$el` references for this view using the
          // given `el`. `el` can be a CSS selector or an HTML string, a jQuery
          // context or an element. Subclasses can override this to utilize an
          // alternative DOM manipulation API and are only required to set the
          // `this.el` property.
          _setElement: function(el) {
              this.$el = el instanceof Backbone.$ ? el : Backbone.$(el);
              this.el = this.$el[0];
          },
  
          // Set callbacks, where `this.events` is a hash of
          //
          // *{"event selector": "callback"}*
          //
          //     {
          //       'mousedown .title':  'edit',
          //       'click .button':     'save',
          //       'click .open':       function(e) { ... }
          //     }
          //
          // pairs. Callbacks will be bound to the view, with `this` set properly.
          // Uses event delegation for efficiency.
          // Omitting the selector binds the event to `this.el`.
          delegateEvents: function(events) {
              if (!(events || (events = _.result(this, 'events')))) return this;
              this.undelegateEvents();
              for (var key in events) {
                  var method = events[key];
                  if (!_.isFunction(method)) method = this[events[key]];
                  if (!method) continue;
                  var match = key.match(delegateEventSplitter);
                  this.delegate(match[1], match[2], _.bind(method, this));
              }
              return this;
          },
  
          // Add a single event listener to the view's element (or a child element
          // using `selector`). This only works for delegate-able events: not `focus`,
          // `blur`, and not `change`, `submit`, and `reset` in Internet Explorer.
          delegate: function(eventName, selector, listener) {
              this.$el.on(eventName + '.delegateEvents' + this.cid, selector, listener);
          },
  
          // Clears all callbacks previously bound to the view by `delegateEvents`.
          // You usually don't need to use this, but may wish to if you have multiple
          // Backbone views attached to the same DOM element.
          undelegateEvents: function() {
              if (this.$el) this.$el.off('.delegateEvents' + this.cid);
              return this;
          },
  
          // A finer-grained `undelegateEvents` for removing a single delegated event.
          // `selector` and `listener` are both optional.
          undelegate: function(eventName, selector, listener) {
              this.$el.off(eventName + '.delegateEvents' + this.cid, selector, listener);
          },
  
          // Produces a DOM element to be assigned to your view. Exposed for
          // subclasses using an alternative DOM manipulation API.
          _createElement: function(tagName) {
              return document.createElement(tagName);
          },
  
          // Ensure that the View has a DOM element to render into.
          // If `this.el` is a string, pass it through `$()`, take the first
          // matching element, and re-assign it to `el`. Otherwise, create
          // an element from the `id`, `className` and `tagName` properties.
          _ensureElement: function() {
              if (!this.el) {
                  var attrs = _.extend({}, _.result(this, 'attributes'));
                  if (this.id) attrs.id = _.result(this, 'id');
                  if (this.className) attrs['class'] = _.result(this, 'className');
                  this.setElement(this._createElement(_.result(this, 'tagName')));
                  this._setAttributes(attrs);
              } else {
                  this.setElement(_.result(this, 'el'));
              }
          },
  
          // Set attributes from a hash on this view's element.  Exposed for
          // subclasses using an alternative DOM manipulation API.
          _setAttributes: function(attributes) {
              this.$el.attr(attributes);
          }
  
      });
  
      // Backbone.sync
      // -------------
  
      // Override this function to change the manner in which Backbone persists
      // models to the server. You will be passed the type of request, and the
      // model in question. By default, makes a RESTful Ajax request
      // to the model's `url()`. Some possible customizations could be:
      //
      // * Use `setTimeout` to batch rapid-fire updates into a single request.
      // * Send up the models as XML instead of JSON.
      // * Persist models via WebSockets instead of Ajax.
      //
      // Turn on `Backbone.emulateHTTP` in order to send `PUT` and `DELETE` requests
      // as `POST`, with a `_method` parameter containing the true HTTP method,
      // as well as all requests with the body as `application/x-www-form-urlencoded`
      // instead of `application/json` with the model in a param named `model`.
      // Useful when interfacing with server-side languages like **PHP** that make
      // it difficult to read the body of `PUT` requests.
      Backbone.sync = function(method, model, options) {
          var type = methodMap[method];
  
          // Default options, unless specified.
          _.defaults(options || (options = {}), {
              emulateHTTP: Backbone.emulateHTTP,
              emulateJSON: Backbone.emulateJSON
          });
  
          // Default JSON-request options.
          var params = {type: type, dataType: 'json'};
  
          // Ensure that we have a URL.
          if (!options.url) {
              params.url = _.result(model, 'url') || urlError();
          }
  
          // Ensure that we have the appropriate request data.
          if (options.data == null && model && (method === 'create' || method === 'update' || method === 'patch')) {
              params.contentType = 'application/json';
              params.data = JSON.stringify(options.attrs || model.toJSON(options));
          }
  
          // For older servers, emulate JSON by encoding the request into an HTML-form.
          if (options.emulateJSON) {
              params.contentType = 'application/x-www-form-urlencoded';
              params.data = params.data ? {model: params.data} : {};
          }
  
          // For older servers, emulate HTTP by mimicking the HTTP method with `_method`
          // And an `X-HTTP-Method-Override` header.
          if (options.emulateHTTP && (type === 'PUT' || type === 'DELETE' || type === 'PATCH')) {
              params.type = 'POST';
              if (options.emulateJSON) params.data._method = type;
              var beforeSend = options.beforeSend;
              options.beforeSend = function(xhr) {
                  xhr.setRequestHeader('X-HTTP-Method-Override', type);
                  if (beforeSend) return beforeSend.apply(this, arguments);
              };
          }
  
          // Don't process data on a non-GET request.
          if (params.type !== 'GET' && !options.emulateJSON) {
              params.processData = false;
          }
  
          // Pass along `textStatus` and `errorThrown` from jQuery.
          var error = options.error;
          options.error = function(xhr, textStatus, errorThrown) {
              options.textStatus = textStatus;
              options.errorThrown = errorThrown;
              if (error) error.call(options.context, xhr, textStatus, errorThrown);
          };
  
          // Make the request, allowing the user to override any Ajax options.
          var xhr = options.xhr = Backbone.ajax(_.extend(params, options));
          model.trigger('request', model, xhr, options);
          return xhr;
      };
  
      // Map from CRUD to HTTP for our default `Backbone.sync` implementation.
      var methodMap = {
          'create': 'POST',
          'update': 'PUT',
          'patch':  'PATCH',
          'delete': 'DELETE',
          'read':   'GET'
      };
  
      // Set the default implementation of `Backbone.ajax` to proxy through to `$`.
      // Override this if you'd like to use a different library.
      Backbone.ajax = function() {
          return Backbone.$.ajax.apply(Backbone.$, arguments);
      };
  
      // Backbone.Router
      // ---------------
  
      // Routers map faux-URLs to actions, and fire events when routes are
      // matched. Creating a new one sets its `routes` hash, if not set statically.
      var Router = Backbone.Router = function(options) {
          options || (options = {});
          if (options.routes) this.routes = options.routes;
          this._bindRoutes();
          this.initialize.apply(this, arguments);
      };
  
      // Cached regular expressions for matching named param parts and splatted
      // parts of route strings.
      var optionalParam = /\((.*?)\)/g;
      var namedParam    = /(\(\?)?:\w+/g;
      var splatParam    = /\*\w+/g;
      var escapeRegExp  = /[\-{}\[\]+?.,\\\^$|#\s]/g;
  
      // Set up all inheritable **Backbone.Router** properties and methods.
      _.extend(Router.prototype, Events, {
  
          // Initialize is an empty function by default. Override it with your own
          // initialization logic.
          initialize: function(){},
  
          // Manually bind a single named route to a callback. For example:
          //
          //     this.route('search/:query/p:num', 'search', function(query, num) {
          //       ...
          //     });
          //
          route: function(route, name, callback) {
              if (!_.isRegExp(route)) route = this._routeToRegExp(route);
              if (_.isFunction(name)) {
                  callback = name;
                  name = '';
              }
              if (!callback) callback = this[name];
              var router = this;
              Backbone.history.route(route, function(fragment) {
                  var args = router._extractParameters(route, fragment);
                  if (router.execute(callback, args, name) !== false) {
                      router.trigger.apply(router, ['route:' + name].concat(args));
                      router.trigger('route', name, args);
                      Backbone.history.trigger('route', router, name, args);
                  }
              });
              return this;
          },
  
          // Execute a route handler with the provided parameters.  This is an
          // excellent place to do pre-route setup or post-route cleanup.
          execute: function(callback, args, name) {
              if (callback) callback.apply(this, args);
          },
  
          // Simple proxy to `Backbone.history` to save a fragment into the history.
          navigate: function(fragment, options) {
              Backbone.history.navigate(fragment, options);
              return this;
          },
  
          // Bind all defined routes to `Backbone.history`. We have to reverse the
          // order of the routes here to support behavior where the most general
          // routes can be defined at the bottom of the route map.
          _bindRoutes: function() {
              if (!this.routes) return;
              this.routes = _.result(this, 'routes');
              var route, routes = _.keys(this.routes);
              while ((route = routes.pop()) != null) {
                  this.route(route, this.routes[route]);
              }
          },
  
          // Convert a route string into a regular expression, suitable for matching
          // against the current location hash.
          _routeToRegExp: function(route) {
              route = route.replace(escapeRegExp, '\\$&')
                  .replace(optionalParam, '(?:$1)?')
                  .replace(namedParam, function(match, optional) {
                      return optional ? match : '([^/?]+)';
                  })
                  .replace(splatParam, '([^?]*?)');
              return new RegExp('^' + route + '(?:\\?([\\s\\S]*))?$');
          },
  
          // Given a route, and a URL fragment that it matches, return the array of
          // extracted decoded parameters. Empty or unmatched parameters will be
          // treated as `null` to normalize cross-browser behavior.
          _extractParameters: function(route, fragment) {
              var params = route.exec(fragment).slice(1);
              return _.map(params, function(param, i) {
                  // Don't decode the search params.
                  if (i === params.length - 1) return param || null;
                  return param ? decodeURIComponent(param) : null;
              });
          }
  
      });
  
      // Backbone.History
      // ----------------
  
      // Handles cross-browser history management, based on either
      // [pushState](http://diveintohtml5.info/history.html) and real URLs, or
      // [onhashchange](https://developer.mozilla.org/en-US/docs/DOM/window.onhashchange)
      // and URL fragments. If the browser supports neither (old IE, natch),
      // falls back to polling.
      var History = Backbone.History = function() {
          this.handlers = [];
          _.bindAll(this, 'checkUrl');
  
          // Ensure that `History` can be used outside of the browser.
          if (typeof window !== 'undefined') {
              this.location = window.location;
              this.history = window.history;
          }
      };
  
      // Cached regex for stripping a leading hash/slash and trailing space.
      var routeStripper = /^[#\/]|\s+$/g;
  
      // Cached regex for stripping leading and trailing slashes.
      var rootStripper = /^\/+|\/+$/g;
  
      // Cached regex for stripping urls of hash.
      var pathStripper = /#.*$/;
  
      // Has the history handling already been started?
      History.started = false;
  
      // Set up all inheritable **Backbone.History** properties and methods.
      _.extend(History.prototype, Events, {
  
          // The default interval to poll for hash changes, if necessary, is
          // twenty times a second.
          interval: 50,
  
          // Are we at the app root?
          atRoot: function() {
              var path = this.location.pathname.replace(/[^\/]$/, '$&/');
              return path === this.root && !this.getSearch();
          },
  
          // Does the pathname match the root?
          matchRoot: function() {
              var path = this.decodeFragment(this.location.pathname);
              var root = path.slice(0, this.root.length - 1) + '/';
              return root === this.root;
          },
  
          // Unicode characters in `location.pathname` are percent encoded so they're
          // decoded for comparison. `%25` should not be decoded since it may be part
          // of an encoded parameter.
          decodeFragment: function(fragment) {
              return decodeURI(fragment.replace(/%25/g, '%2525'));
          },
  
          // In IE6, the hash fragment and search params are incorrect if the
          // fragment contains `?`.
          getSearch: function() {
              var match = this.location.href.replace(/#.*/, '').match(/\?.+/);
              return match ? match[0] : '';
          },
  
          // Gets the true hash value. Cannot use location.hash directly due to bug
          // in Firefox where location.hash will always be decoded.
          getHash: function(window) {
              var match = (window || this).location.href.match(/#(.*)$/);
              return match ? match[1] : '';
          },
  
          // Get the pathname and search params, without the root.
          getPath: function() {
              var path = this.decodeFragment(
                  this.location.pathname + this.getSearch()
              ).slice(this.root.length - 1);
              return path.charAt(0) === '/' ? path.slice(1) : path;
          },
  
          // Get the cross-browser normalized URL fragment from the path or hash.
          getFragment: function(fragment) {
              if (fragment == null) {
                  if (this._usePushState || !this._wantsHashChange) {
                      fragment = this.getPath();
                  } else {
                      fragment = this.getHash();
                  }
              }
              return fragment.replace(routeStripper, '');
          },
  
          // Start the hash change handling, returning `true` if the current URL matches
          // an existing route, and `false` otherwise.
          start: function(options) {
              if (History.started) throw new Error('Backbone.history has already been started');
              History.started = true;
  
              // Figure out the initial configuration. Do we need an iframe?
              // Is pushState desired ... is it available?
              this.options          = _.extend({root: '/'}, this.options, options);
              this.root             = this.options.root;
              this._wantsHashChange = this.options.hashChange !== false;
              this._hasHashChange   = 'onhashchange' in window;
              this._useHashChange   = this._wantsHashChange && this._hasHashChange;
              this._wantsPushState  = !!this.options.pushState;
              this._hasPushState    = !!(this.history && this.history.pushState);
              this._usePushState    = this._wantsPushState && this._hasPushState;
              this.fragment         = this.getFragment();
  
              // Normalize root to always include a leading and trailing slash.
              this.root = ('/' + this.root + '/').replace(rootStripper, '/');
  
              // Transition from hashChange to pushState or vice versa if both are
              // requested.
              if (this._wantsHashChange && this._wantsPushState) {
  
                  // If we've started off with a route from a `pushState`-enabled
                  // browser, but we're currently in a browser that doesn't support it...
                  if (!this._hasPushState && !this.atRoot()) {
                      var root = this.root.slice(0, -1) || '/';
                      this.location.replace(root + '#' + this.getPath());
                      // Return immediately as browser will do redirect to new url
                      return true;
  
                      // Or if we've started out with a hash-based route, but we're currently
                      // in a browser where it could be `pushState`-based instead...
                  } else if (this._hasPushState && this.atRoot()) {
                      this.navigate(this.getHash(), {replace: true});
                  }
  
              }
  
              // Proxy an iframe to handle location events if the browser doesn't
              // support the `hashchange` event, HTML5 history, or the user wants
              // `hashChange` but not `pushState`.
              if (!this._hasHashChange && this._wantsHashChange && !this._usePushState) {
                  var iframe = document.createElement('iframe');
                  iframe.src = 'javascript:0';
                  iframe.style.display = 'none';
                  iframe.tabIndex = -1;
                  var body = document.body;
                  // Using `appendChild` will throw on IE < 9 if the document is not ready.
                  this.iframe = body.insertBefore(iframe, body.firstChild).contentWindow;
                  this.iframe.document.open().close();
                  this.iframe.location.hash = '#' + this.fragment;
              }
  
              // Add a cross-platform `addEventListener` shim for older browsers.
              var addEventListener = window.addEventListener || function (eventName, listener) {
                      return attachEvent('on' + eventName, listener);
                  };
  
              // Depending on whether we're using pushState or hashes, and whether
              // 'onhashchange' is supported, determine how we check the URL state.
              if (this._usePushState) {
                  addEventListener('popstate', this.checkUrl, false);
              } else if (this._useHashChange && !this.iframe) {
                  addEventListener('hashchange', this.checkUrl, false);
              } else if (this._wantsHashChange) {
                  this._checkUrlInterval = setInterval(this.checkUrl, this.interval);
              }
  
              if (!this.options.silent) return this.loadUrl();
          },
  
          // Disable Backbone.history, perhaps temporarily. Not useful in a real app,
          // but possibly useful for unit testing Routers.
          stop: function() {
              // Add a cross-platform `removeEventListener` shim for older browsers.
              var removeEventListener = window.removeEventListener || function (eventName, listener) {
                      return detachEvent('on' + eventName, listener);
                  };
  
              // Remove window listeners.
              if (this._usePushState) {
                  removeEventListener('popstate', this.checkUrl, false);
              } else if (this._useHashChange && !this.iframe) {
                  removeEventListener('hashchange', this.checkUrl, false);
              }
  
              // Clean up the iframe if necessary.
              if (this.iframe) {
                  document.body.removeChild(this.iframe.frameElement);
                  this.iframe = null;
              }
  
              // Some environments will throw when clearing an undefined interval.
              if (this._checkUrlInterval) clearInterval(this._checkUrlInterval);
              History.started = false;
          },
  
          // Add a route to be tested when the fragment changes. Routes added later
          // may override previous routes.
          route: function(route, callback) {
              this.handlers.unshift({route: route, callback: callback});
          },
  
          // Checks the current URL to see if it has changed, and if it has,
          // calls `loadUrl`, normalizing across the hidden iframe.
          checkUrl: function(e) {
              var current = this.getFragment();
  
              // If the user pressed the back button, the iframe's hash will have
              // changed and we should use that for comparison.
              if (current === this.fragment && this.iframe) {
                  current = this.getHash(this.iframe);
              }
  
              if (current === this.fragment) return false;
              if (this.iframe) this.navigate(current);
              this.loadUrl();
          },
  
          // Attempt to load the current URL fragment. If a route succeeds with a
          // match, returns `true`. If no defined routes matches the fragment,
          // returns `false`.
          loadUrl: function(fragment) {
              // If the root doesn't match, no routes can match either.
              if (!this.matchRoot()) return false;
              fragment = this.fragment = this.getFragment(fragment);
              return _.any(this.handlers, function(handler) {
                  if (handler.route.test(fragment)) {
                      handler.callback(fragment);
                      return true;
                  }
              });
          },
  
          // Save a fragment into the hash history, or replace the URL state if the
          // 'replace' option is passed. You are responsible for properly URL-encoding
          // the fragment in advance.
          //
          // The options object can contain `trigger: true` if you wish to have the
          // route callback be fired (not usually desirable), or `replace: true`, if
          // you wish to modify the current URL without adding an entry to the history.
          navigate: function(fragment, options) {
              if (!History.started) return false;
              if (!options || options === true) options = {trigger: !!options};
  
              // Normalize the fragment.
              fragment = this.getFragment(fragment || '');
  
              // Don't include a trailing slash on the root.
              var root = this.root;
              if (fragment === '' || fragment.charAt(0) === '?') {
                  root = root.slice(0, -1) || '/';
              }
              var url = root + fragment;
  
              // Strip the hash and decode for matching.
              fragment = this.decodeFragment(fragment.replace(pathStripper, ''));
  
              if (this.fragment === fragment) return;
              this.fragment = fragment;
  
              // If pushState is available, we use it to set the fragment as a real URL.
              if (this._usePushState) {
                  this.history[options.replace ? 'replaceState' : 'pushState']({}, document.title, url);
  
                  // If hash changes haven't been explicitly disabled, update the hash
                  // fragment to store history.
              } else if (this._wantsHashChange) {
                  this._updateHash(this.location, fragment, options.replace);
                  if (this.iframe && (fragment !== this.getHash(this.iframe))) {
                      // Opening and closing the iframe tricks IE7 and earlier to push a
                      // history entry on hash-tag change.  When replace is true, we don't
                      // want this.
                      if (!options.replace) this.iframe.document.open().close();
                      this._updateHash(this.iframe.location, fragment, options.replace);
                  }
  
                  // If you've told us that you explicitly don't want fallback hashchange-
                  // based history, then `navigate` becomes a page refresh.
              } else {
                  return this.location.assign(url);
              }
              if (options.trigger) return this.loadUrl(fragment);
          },
  
          // Update the hash location, either replacing the current entry, or adding
          // a new one to the browser history.
          _updateHash: function(location, fragment, replace) {
              if (replace) {
                  var href = location.href.replace(/(javascript:|#).*$/, '');
                  location.replace(href + '#' + fragment);
              } else {
                  // Some browsers require that `hash` contains a leading #.
                  location.hash = '#' + fragment;
              }
          }
  
      });
  
      // Create the default Backbone.history.
      Backbone.history = new History;
  
      // Helpers
      // -------
  
      // Helper function to correctly set up the prototype chain for subclasses.
      // Similar to `goog.inherits`, but uses a hash of prototype properties and
      // class properties to be extended.
      var extend = function(protoProps, staticProps) {
          var parent = this;
          var child;
  
          // The constructor function for the new subclass is either defined by you
          // (the "constructor" property in your `extend` definition), or defaulted
          // by us to simply call the parent constructor.
          if (protoProps && _.has(protoProps, 'constructor')) {
              child = protoProps.constructor;
          } else {
              child = function(){ return parent.apply(this, arguments); };
          }
  
          // Add static properties to the constructor function, if supplied.
          _.extend(child, parent, staticProps);
  
          // Set the prototype chain to inherit from `parent`, without calling
          // `parent` constructor function.
          var Surrogate = function(){ this.constructor = child; };
          Surrogate.prototype = parent.prototype;
          child.prototype = new Surrogate;
  
          // Add prototype properties (instance properties) to the subclass,
          // if supplied.
          if (protoProps) _.extend(child.prototype, protoProps);
  
          // Set a convenience property in case the parent's prototype is needed
          // later.
          child.__super__ = parent.prototype;
  
          return child;
      };
  
      // Set up inheritance for the model, collection, router, view and history.
      Model.extend = Collection.extend = Router.extend = View.extend = History.extend = extend;
  
      // Throw an error when a URL is needed, and none is supplied.
      var urlError = function() {
          throw new Error('A "url" property or function must be specified');
      };
  
      // Wrap an optional error callback with a fallback error event.
      var wrapError = function(model, options) {
          var error = options.error;
          options.error = function(resp) {
              if (error) error.call(options.context, model, resp, options);
              model.trigger('error', model, resp, options);
          };
      };
  
      return Backbone;
  
  }));