text: //     Backbone.js 1.3.3
  
  //     (c) 2010-2016 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 a local reference to a common array method we'll want to use later.
    var slice = Array.prototype.slice;
  
    // Current version of the library. Keep in sync with `package.json`.
    Backbone.VERSION = '1.3.3';
  
    // 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;
  
    // Proxy Backbone class methods to Underscore functions, wrapping the model's
    // `attributes` object or collection's `models` array behind the scenes.
    //
    // collection.filter(function(model) { return model.get('age') > 10 });
    // collection.each(this.addView);
    //
    // `Function#apply` can be slow so we use the method's arg count, if we know it.
    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], cb(iteratee, this), context);
        };
        case 4: return function(iteratee, defaultVal, context) {
          return _[method](this[attribute], cb(iteratee, this), 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);
      });
    };
  
    // Support `collection.sortBy('attr')` and `collection.findWhere({id: 1})`.
    var cb = function(iteratee, instance) {
      if (_.isFunction(iteratee)) return iteratee;
      if (_.isObject(iteratee) && !instance._isModel(iteratee)) return modelMatcher(iteratee);
      if (_.isString(iteratee)) return function(model) { return model.get(iteratee); };
      return iteratee;
    };
    var modelMatcher = function(attrs) {
      var matcher = _.matches(attrs);
      return function(model) {
        return matcher(model.attributes);
      };
    };
  
    // Backbone.Events
    // ---------------
  
    // A module that can be mixed in to *any object* in order to provide it with
    // a custom event channel. You may bind a callback to an event with `on` or
    // remove with `off`; `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}`).
    var eventsApi = function(iteratee, events, name, callback, opts) {
      var i = 0, names;
      if (name && typeof name === 'object') {
        // Handle event maps.
        if (callback !== void 0 && 'context' in opts && opts.context === void 0) opts.context = callback;
        for (names = _.keys(name); i < names.length ; i++) {
          events = eventsApi(iteratee, events, names[i], name[names[i]], opts);
        }
      } else if (name && eventSplitter.test(name)) {
        // Handle space-separated event names by delegating them individually.
        for (names = name.split(eventSplitter); i < names.length; i++) {
          events = iteratee(events, names[i], callback, opts);
        }
      } else {
        // Finally, standard events.
        events = iteratee(events, name, callback, opts);
      }
      return events;
    };
  
    // 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);
    };
  
    // 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
    // for easier unbinding later.
    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);
      }
  
      return this;
    };
  
    // The reducing API that removes a callback from the `events` object.
    var offApi = function(events, name, callback, options) {
      if (!events) return;
  
      var i = 0, 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];
        }
      }
      return events;
    };
  
    // Bind an event to only be triggered a single time. After the first time
    // the callback is invoked, its listener will be removed. If multiple events
    // are passed in using the space-separated syntax, the handler will fire
    // once for each event, 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));
      if (typeof name === 'string' && context == null) callback = void 0;
      return this.on(events, callback, 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 has 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, callback, 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;
      }
    };
  
    // 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) || {};
      var defaults = _.result(this, 'defaults');
      attrs = _.defaults(_.extend({}, defaults, attrs), 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) {
        if (key == null) return this;
  
        // Handle both `"key", value` and `{key: value}` -style arguments.
        var attrs;
        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.
        var unset      = options.unset;
        var silent     = options.silent;
        var changes    = [];
        var changing   = this._changing;
        this._changing = true;
  
        if (!changing) {
          this._previousAttributes = _.clone(this.attributes);
          this.changed = {};
        }
  
        var current = this.attributes;
        var changed = this.changed;
        var prev    = this._previousAttributes;
  
        // For each `set` attribute, update or delete the current value.
        for (var attr in attrs) {
          val = attrs[attr];
          if (!_.isEqual(current[attr], val)) changes.push(attr);
          if (!_.isEqual(prev[attr], val)) {
            changed[attr] = val;
          } else {
            delete changed[attr];
          }
          unset ? delete current[attr] : current[attr] = val;
        }
  
        // Update the `id`.
        if (this.idAttribute in attrs) this.id = this.get(this.idAttribute);
  
        // 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 old = this._changing ? this._previousAttributes : this.attributes;
        var changed = {};
        for (var attr in diff) {
          var val = diff[attr];
          if (_.isEqual(old[attr], val)) continue;
          changed[attr] = val;
        }
        return _.size(changed) ? changed : false;
      },
  
      // 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 = _.extend({parse: true}, options);
        var model = this;
        var success = options.success;
        options.success = function(resp) {
          var serverAttrs = options.parse ? model.parse(resp, options) : resp;
          if (!model.set(serverAttrs, 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) {
        // Handle both `"key", value` and `{key: value}` -style arguments.
        var attrs;
        if (key == null || typeof key === 'object') {
          attrs = key;
          options = val;
        } else {
          (attrs = {})[key] = val;
        }
  
        options = _.extend({validate: true, parse: true}, options);
        var 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;
        }
  
        // After a successful server-side save, the client is (optionally)
        // updated with the server-side state.
        var model = this;
        var success = options.success;
        var attributes = this.attributes;
        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 (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);
  
        // Set temporary attributes if `{wait: true}` to properly find new ids.
        if (attrs && wait) this.attributes = _.extend({}, attributes, attrs);
  
        var method = this.isNew() ? 'create' : (options.patch ? 'patch' : 'update');
        if (method === 'patch' && !options.attrs) options.attrs = attrs;
        var xhr = this.sync(method, this, options);
  
        // Restore attributes.
        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.get(this.idAttribute);
        return base.replace(/[^\/]$/, '$&/') + 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, mapped to the
    // number of arguments they take.
    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};
  
    // Splices `insert` into `array` at index `at`.
    var splice = function(array, insert, at) {
      at = Math.min(Math.max(at, 0), array.length);
      var tail = Array(array.length - at);
      var length = insert.length;
      var i;
      for (i = 0; i < tail.length; i++) tail[i] = array[i + at];
      for (i = 0; i < length; i++) array[i + at] = insert[i];
      for (i = 0; i < tail.length; i++) array[i + length + at] = tail[i];
    };
  
    // 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. `models` may be Backbone
      // Models or raw JavaScript objects to be converted to Models, or any
      // combination of the two.
      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) {
        options = _.extend({}, options);
        var singular = !_.isArray(models);
        models = singular ? [models] : models.slice();
        var removed = this._removeModels(models, options);
        if (!options.silent && removed.length) {
          options.changes = {added: [], merged: [], removed: removed};
          this.trigger('update', this, options);
        }
        return singular ? removed[0] : removed;
      },
  
      // 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) {
        if (models == null) return;
  
        options = _.extend({}, setOptions, options);
        if (options.parse && !this._isModel(models)) {
          models = this.parse(models, options) || [];
        }
  
        var singular = !_.isArray(models);
        models = singular ? [models] : models.slice();
  
        var at = options.at;
        if (at != null) at = +at;
        if (at > this.length) at = this.length;
        if (at < 0) at += this.length + 1;
  
        var set = [];
        var toAdd = [];
        var toMerge = [];
        var toRemove = [];
        var modelMap = {};
  
        var add = options.add;
        var merge = options.merge;
        var remove = options.remove;
  
        var sort = false;
        var sortable = this.comparator && at == null && options.sort !== false;
        var sortAttr = _.isString(this.comparator) ? this.comparator : null;
  
        // Turn bare objects into model references, and prevent invalid models
        // from being added.
        var model, i;
        for (i = 0; i < models.length; i++) {
          model = models[i];
  
          // If a duplicate is found, prevent it from being added and
          // optionally merge it into the existing model.
          var existing = this.get(model);
          if (existing) {
            if (merge && model !== existing) {
              var attrs = this._isModel(model) ? model.attributes : model;
              if (options.parse) attrs = existing.parse(attrs, options);
              existing.set(attrs, options);
              toMerge.push(existing);
              if (sortable && !sort) sort = existing.hasChanged(sortAttr);
            }
            if (!modelMap[existing.cid]) {
              modelMap[existing.cid] = true;
              set.push(existing);
            }
            models[i] = existing;
  
          // If this is a new, valid model, push it to the `toAdd` list.
          } else if (add) {
            model = models[i] = this._prepareModel(model, options);
            if (model) {
              toAdd.push(model);
              this._addReference(model, options);
              modelMap[model.cid] = true;
              set.push(model);
            }
          }
        }
  
        // Remove stale models.
        if (remove) {
          for (i = 0; i < this.length; i++) {
            model = this.models[i];
            if (!modelMap[model.cid]) toRemove.push(model);
          }
          if (toRemove.length) this._removeModels(toRemove, options);
        }
  
        // See if sorting is needed, update `length` and splice in new models.
        var orderChanged = false;
        var replace = !sortable && add && remove;
        if (set.length && replace) {
          orderChanged = this.length !== set.length || _.some(this.models, function(m, index) {
            return m !== set[index];
          });
          this.models.length = 0;
          splice(this.models, set, 0);
          this.length = this.models.length;
        } else if (toAdd.length) {
          if (sortable) sort = true;
          splice(this.models, toAdd, at == null ? this.length : at);
          this.length = this.models.length;
        }
  
        // Silently sort the collection if appropriate.
        if (sort) this.sort({silent: true});
  
        // Unless silenced, it's time to fire all appropriate add/sort/update events.
        if (!options.silent) {
          for (i = 0; i < toAdd.length; i++) {
            if (at != null) options.index = at + i;
            model = toAdd[i];
            model.trigger('add', model, this, options);
          }
          if (sort || orderChanged) this.trigger('sort', this, options);
          if (toAdd.length || toRemove.length || toMerge.length) {
            options.changes = {
              added: toAdd,
              removed: toRemove,
              merged: toMerge
            };
            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);
        return this.remove(model, options);
      },
  
      // 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);
        return this.remove(model, options);
      },
  
      // 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, cid, model object with id or cid
      // properties, or an attributes object that is transformed through modelId.
      get: function(obj) {
        if (obj == null) return void 0;
        return this._byId[obj] ||
          this._byId[this.modelId(obj.attributes || obj)] ||
          obj.cid && this._byId[obj.cid];
      },
  
      // Returns `true` if the model is in the collection.
      has: function(obj) {
        return this.get(obj) != null;
      },
  
      // 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) {
        return this[first ? 'find' : 'filter'](attrs);
      },
  
      // 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) {
        var comparator = this.comparator;
        if (!comparator) throw new Error('Cannot sort a set without a comparator');
        options || (options = {});
  
        var length = comparator.length;
        if (_.isFunction(comparator)) comparator = _.bind(comparator, this);
  
        // Run sort based on type of `comparator`.
        if (length === 1 || _.isString(comparator)) {
          this.models = this.sortBy(comparator);
        } else {
          this.models.sort(comparator);
        }
        if (!options.silent) this.trigger('sort', this, options);
        return this;
      },
  
      // Pluck an attribute from each model in the collection.
      pluck: function(attr) {
        return this.map(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 = _.extend({parse: true}, options);
        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;
        model = this._prepareModel(model, options);
        if (!model) return false;
        if (!wait) this.add(model, options);
        var collection = this;
        var success = options.success;
        options.success = function(m, resp, callbackOpts) {
          if (wait) collection.add(m, callbackOpts);
          if (success) success.call(callbackOpts.context, m, 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.
      _removeModels: function(models, options) {
        var removed = [];
        for (var i = 0; i < models.length; i++) {
          var model = this.get(models[i]);
          if (!model) continue;
  
          var index = this.indexOf(model);
          this.models.splice(index, 1);
          this.length--;
  
          // Remove references before triggering 'remove' event to prevent an
          // infinite loop. #3693
          delete this._byId[model.cid];
          var id = this.modelId(model.attributes);
          if (id != null) delete this._byId[id];
  
          if (!options.silent) {
            options.index = index;
            model.trigger('remove', model, this, options);
          }
  
          removed.push(model);
          this._removeReference(model, options);
        }
        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) {
        delete this._byId[model.cid];
        var id = this.modelId(model.attributes);
        if (id != null) delete this._byId[id];
        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 (model) {
          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: 0,
        foldl: 0, inject: 0, reduceRight: 0, foldr: 0, find: 3, detect: 3, filter: 3,
        select: 3, reject: 3, every: 3, all: 3, some: 3, any: 3, include: 3, includes: 3,
        contains: 3, invoke: 0, 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, groupBy: 3, countBy: 3,
        sortBy: 3, indexBy: 3, findIndex: 3, findLastIndex: 3};
  
    // Mix in each Underscore method as a proxy to `Collection#models`.
    addUnderscoreMethods(Collection, collectionMethods, 'models');
  
    // 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');
      _.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 set 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) {
        events || (events = _.result(this, 'events'));
        if (!events) return this;
        this.undelegateEvents();
        for (var key in events) {
          var method = events[key];
          if (!_.isFunction(method)) method = this[method];
          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);
        return this;
      },
  
      // 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);
        return this;
      },
  
      // 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 = [];
      this.checkUrl = _.bind(this.checkUrl, this);
  
      // 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 rootPath = path.slice(0, this.root.length - 1) + '/';
        return rootPath === 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 && (document.documentMode === void 0 || document.documentMode > 7);
        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 rootPath = this.root.slice(0, -1) || '/';
            this.location.replace(rootPath + '#' + 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) {
          this.iframe = document.createElement('iframe');
          this.iframe.src = 'javascript:0';
          this.iframe.style.display = 'none';
          this.iframe.tabIndex = -1;
          var body = document.body;
          // Using `appendChild` will throw on IE < 9 if the document is not ready.
          var iWindow = body.insertBefore(this.iframe, body.firstChild).contentWindow;
          iWindow.document.open();
          iWindow.document.close();
          iWindow.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.
        debugger
        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);
          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) {
        debugger
        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.contentWindow);
        }
  
        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 _.some(this.handlers, function(handler) {
          if (handler.route.test(fragment)) {
            debugger
            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 rootPath = this.root;
        if (fragment === '' || fragment.charAt(0) === '?') {
          rootPath = rootPath.slice(0, -1) || '/';
        }
        var url = rootPath + 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.contentWindow)) {
            var iWindow = this.iframe.contentWindow;
  
            // 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) {
              iWindow.document.open();
              iWindow.document.close();
            }
  
            this._updateHash(iWindow.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`'s constructor function and add the prototype properties.
      child.prototype = _.create(parent.prototype, protoProps);
      child.prototype.constructor = child;
  
      // 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;
  });
  