//     Backbone.js 1.1.2

//     (c) 2010-2014 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(root, factory) {

    // 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');
        factory(root, exports, _);

        // Finally, as a browser global.
    } else {
        root.Backbone = factory(root, {}, root._, (root.jQuery || root.Zepto || root.ender || root.$));
    }

}(this, 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 push = array.push;
    var slice = array.slice;
    var splice = array.splice;

    // Current version of the library. Keep in sync with `package.json`.
    Backbone.VERSION = '1.1.2';

    // 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 ... 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 = {

        // Bind an event to a `callback` function. Passing `"all"` will bind
        // the callback to all events fired.
        on: function(name, callback, context) {
            if (!eventsApi(this, 'on', name, [callback, context]) || !callback) return this;
            this._events || (this._events = {});
            var events = this._events[name] || (this._events[name] = []);
            events.push({callback: callback, context: context, ctx: context || this});
            return this;
        },

        // Bind an event to only be triggered a single time. After the first time
        // the callback is invoked, it will be removed.
        once: function(name, callback, context) {
            if (!eventsApi(this, 'once', name, [callback, context]) || !callback) return this;
            var self = this;
            var once = _.once(function() {
                self.off(name, once);
                callback.apply(this, arguments);
            });
            once._callback = callback;
            return this.on(name, once, context);
        },

        // 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.
        off: function(name, callback, context) {
            var retain, ev, events, names, i, l, j, k;
            if (!this._events || !eventsApi(this, 'off', name, [callback, context])) return this;
            if (!name && !callback && !context) {
                this._events = void 0;
                return this;
            }
            names = name ? [name] : _.keys(this._events);
            for (i = 0, l = names.length; i < l; i++) {
                name = names[i];
                if (events = this._events[name]) {
                    this._events[name] = retain = [];
                    if (callback || context) {
                        for (j = 0, k = events.length; j < k; j++) {
                            ev = events[j];
                            if ((callback && callback !== ev.callback && callback !== ev.callback._callback) ||
                                (context && context !== ev.context)) {
                                retain.push(ev);
                            }
                        }
                    }
                    if (!retain.length) delete this._events[name];
                }
            }

            return this;
        },

        // 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).
        trigger: function(name) {
            if (!this._events) return this;
            var args = slice.call(arguments, 1);
            if (!eventsApi(this, 'trigger', name, args)) return this;
            var events = this._events[name];
            var allEvents = this._events.all;
            if (events) triggerEvents(events, args);
            if (allEvents) triggerEvents(allEvents, arguments);
            return this;
        },

        // Tell this object to stop listening to either specific events ... or
        // to every object it's currently listening to.
        stopListening: function(obj, name, callback) {
            var listeningTo = this._listeningTo;
            if (!listeningTo) return this;
            var remove = !name && !callback;
            if (!callback && typeof name === 'object') callback = this;
            if (obj) (listeningTo = {})[obj._listenId] = obj;
            for (var id in listeningTo) {
                obj = listeningTo[id];
                obj.off(name, callback, this);
                if (remove || _.isEmpty(obj._events)) delete this._listeningTo[id];
            }
            return this;
        }

    };

    // Regular expression used to split event strings.
    var eventSplitter = /\s+/;

    // Implement fancy features of the Events API such as multiple event
    // names `"change blur"` and jQuery-style event maps `{change: action}`
    // in terms of the existing API.
    var eventsApi = function(obj, action, name, rest) {
        if (!name) return true;

        // Handle event maps.
        if (typeof name === 'object') {
            for (var key in name) {
                obj[action].apply(obj, [key, name[key]].concat(rest));
            }
            return false;
        }

        // Handle space separated event names.
        if (eventSplitter.test(name)) {
            var names = name.split(eventSplitter);
            for (var i = 0, l = names.length; i < l; i++) {
                obj[action].apply(obj, [names[i]].concat(rest));
            }
            return false;
        }

        return true;
    };

    // 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;
        }
    };

    var listenMethods = {listenTo: 'on', listenToOnce: 'once'};

    // Inversion-of-control versions of `on` and `once`. Tell *this* object to
    // listen to an event in another object ... keeping track of what it's
    // listening to.
    _.each(listenMethods, function(implementation, method) {
        Events[method] = function(obj, name, callback) {
            var listeningTo = this._listeningTo || (this._listeningTo = {});
            var id = obj._listenId || (obj._listenId = _.uniqueId('l'));
            listeningTo[id] = obj;
            if (!callback && typeof name === 'object') callback = this;
            obj[implementation](name, callback, this);
            return this;
        };
    });

    // 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('c');
        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',

        // 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;
        },

        // 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, l = changes.length; i < l; 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. If the server's representation of the
        // model differs from its current attributes, they will be overridden,
        // triggering 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(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;

            // 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);

            // 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 && !options.wait) {
                if (!this.set(attrs, options)) return false;
            } else {
                if (!this._validate(attrs, options)) return false;
            }

            // Set temporary attributes if `{wait: true}`.
            if (attrs && options.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 = model.parse(resp, options);
                if (options.wait) serverAttrs = _.extend(attrs || {}, serverAttrs);
                if (_.isObject(serverAttrs) && !model.set(serverAttrs, options)) {
                    return false;
                }
                if (success) success(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 = attrs;
            xhr = this.sync(method, this, options);

            // Restore attributes.
            if (attrs && options.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 destroy = function() {
                model.trigger('destroy', model, model.collection, options);
            };

            options.success = function(resp) {
                if (options.wait || model.isNew()) destroy();
                if (success) success(model, resp, options);
                if (!model.isNew()) model.trigger('sync', model, resp, options);
            };

            if (this.isNew()) {
                options.success();
                return false;
            }
            wrapError(this, options);

            var xhr = this.sync('delete', this, options);
            if (!options.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;
            return base.replace(/([^\/])$/, '$1/') + encodeURIComponent(this.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', 'values', 'pairs', 'invert', 'pick', 'omit'];

    // Mix in each Underscore method as a proxy to `Model#attributes`.
    _.each(modelMethods, function(method) {
        Model.prototype[method] = function() {
            var args = slice.call(arguments);
            args.unshift(this.attributes);
            return _[method].apply(_, args);
        };
    });

    // Backbone.Collection
    // -------------------

    // If models tend to represent a single row of data, a Backbone Collection is
    // more analagous 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);
            models = singular ? [models] : _.clone(models);
            options || (options = {});
            var i, l, index, model;
            for (i = 0, l = models.length; i < l; i++) {
                model = models[i] = this.get(models[i]);
                if (!model) continue;
                delete this._byId[model.id];
                delete this._byId[model.cid];
                index = this.indexOf(model);
                this.models.splice(index, 1);
                this.length--;
                if (!options.silent) {
                    options.index = index;
                    model.trigger('remove', model, this, options);
                }
                this._removeReference(model, 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] : []) : _.clone(models);
            var i, l, id, model, attrs, existing, sort;
            var at = options.at;
            var targetModel = this.model;
            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;

            // Turn bare objects into model references, and prevent invalid models
            // from being added.
            for (i = 0, l = models.length; i < l; i++) {
                attrs = models[i] || {};
                if (attrs instanceof Model) {
                    id = model = attrs;
                } else {
                    id = attrs[targetModel.prototype.idAttribute || 'id'];
                }

                // If a duplicate is found, prevent it from being added and
                // optionally merge it into the existing model.
                if (existing = this.get(id)) {
                    if (remove) modelMap[existing.cid] = true;
                    if (merge) {
                        attrs = attrs === model ? model.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 (order && (model.isNew() || !modelMap[model.id])) order.push(model);
                modelMap[model.id] = true;
            }

            // Remove nonexistent models if appropriate.
            if (remove) {
                for (i = 0, l = this.length; i < l; ++i) {
                    if (!modelMap[(model = this.models[i]).cid]) toRemove.push(model);
                }
                if (toRemove.length) this.remove(toRemove, options);
            }

            // See if sorting is needed, update `length` and splice in new models.
            if (toAdd.length || (order && order.length)) {
                if (sortable) sort = true;
                this.length += toAdd.length;
                if (at != null) {
                    for (i = 0, l = toAdd.length; i < l; i++) {
                        this.models.splice(at + i, 0, toAdd[i]);
                    }
                } else {
                    if (order) this.models.length = 0;
                    var orderedModels = order || toAdd;
                    for (i = 0, l = orderedModels.length; i < l; 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) {
                for (i = 0, l = toAdd.length; i < l; i++) {
                    (model = toAdd[i]).trigger('add', model, this, options);
                }
                if (sort || (order && order.length)) this.trigger('sort', 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 = {});
            for (var i = 0, l = this.models.length; i < l; 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;
            return this._byId[obj] || this._byId[obj.id] || this._byId[obj.cid];
        },

        // Get the model at the given index.
        at: function(index) {
            return this.models[index];
        },

        // Return models with matching attributes. Useful for simple cases of
        // `filter`.
        where: function(attrs, first) {
            if (_.isEmpty(attrs)) return first ? void 0 : [];
            return this[first ? 'find' : 'filter'](function(model) {
                for (var key in attrs) {
                    if (attrs[key] !== model.get(key)) return false;
                }
                return true;
            });
        },

        // 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(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) : {};
            if (!(model = this._prepareModel(model, options))) return false;
            if (!options.wait) this.add(model, options);
            var collection = this;
            var success = options.success;
            options.success = function(model, resp) {
                if (options.wait) collection.add(model, options);
                if (success) success(model, resp, options);
            };
            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);
        },

        // 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 (attrs instanceof Model) 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 to create a model's ties to a collection.
        _addReference: function(model, options) {
            this._byId[model.cid] = model;
            if (model.id != null) this._byId[model.id] = model;
            if (!model.collection) model.collection = this;
            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 (model && event === 'change:' + model.idAttribute) {
                delete this._byId[model.previous(model.idAttribute)];
                if (model.id != null) this._byId[model.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 methods = ['forEach', 'each', 'map', 'collect', 'reduce', 'foldl',
        'inject', 'reduceRight', 'foldr', 'find', 'detect', 'filter', 'select',
        'reject', 'every', 'all', 'some', 'any', 'include', 'contains', 'invoke',
        'max', 'min', 'toArray', 'size', 'first', 'head', 'take', 'initial', 'rest',
        'tail', 'drop', 'last', 'without', 'difference', 'indexOf', 'shuffle',
        'lastIndexOf', 'isEmpty', 'chain', 'sample'];

    // Mix in each Underscore method as a proxy to `Collection#models`.
    _.each(methods, function(method) {
        Collection.prototype[method] = function() {
            var args = slice.call(arguments);
            args.unshift(this.models);
            return _[method].apply(_, args);
        };
    });

    // 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) {
        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);
        this.delegateEvents();
    };

    // 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.$el.remove();
            this.stopListening();
            return this;
        },

        // Change the view's element (`this.el` property), including event
        // re-delegation.
        setElement: function(element, delegate) {
            if (this.$el) this.undelegateEvents();
            this.$el = element instanceof Backbone.$ ? element : Backbone.$(element);
            this.el = this.$el[0];
            if (delegate !== false) this.delegateEvents();
            return this;
        },

        // 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`.
        // This only works for delegate-able events: not `focus`, `blur`, and
        // not `change`, `submit`, and `reset` in Internet Explorer.
        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);
                var eventName = match[1], selector = match[2];
                method = _.bind(method, this);
                eventName += '.delegateEvents' + this.cid;
                if (selector === '') {
                    this.$el.on(eventName, method);
                } else {
                    this.$el.on(eventName, selector, method);
                }
            }
            return this;
        },

        // Clears all callbacks previously bound to the view with `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() {
            this.$el.off('.delegateEvents' + this.cid);
            return this;
        },

        // 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');
                var $el = Backbone.$('<' + _.result(this, 'tagName') + '>').attr(attrs);
                this.setElement($el, false);
            } else {
                this.setElement(_.result(this, 'el'), false);
            }
        }

    });

    // 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;
        }

        // If we're sending a `PATCH` request, and we're in an old Internet Explorer
        // that still has ActiveX enabled by default, override jQuery to use that
        // for XHR instead. Remove this line when jQuery supports `PATCH` on IE8.
        if (params.type === 'PATCH' && noXhrPatch) {
            params.xhr = function() {
                return new ActiveXObject("Microsoft.XMLHTTP");
            };
        }

        // 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;
    };

    var noXhrPatch =
        typeof window !== 'undefined' && !!window.ActiveXObject &&
        !(window.XMLHttpRequest && (new XMLHttpRequest).dispatchEvent);

    // 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) !== 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) {
            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 detecting MSIE.
    var isExplorer = /msie [\w.]+/;

    // Cached regex for removing a trailing slash.
    var trailingSlash = /\/$/;

    // 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() {
            return this.location.pathname.replace(/[^\/]$/, '$&/') === this.root;
        },

        // 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 cross-browser normalized URL fragment, either from the URL,
        // the hash, or the override.
        getFragment: function(fragment, forcePushState) {
            if (fragment == null) {
                if (this._hasPushState || !this._wantsHashChange || forcePushState) {
                    fragment = decodeURI(this.location.pathname + this.location.search);
                    var root = this.root.replace(trailingSlash, '');
                    if (!fragment.indexOf(root)) fragment = fragment.slice(root.length);
                } 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._wantsPushState  = !!this.options.pushState;
            this._hasPushState    = !!(this.options.pushState && this.history && this.history.pushState);
            var fragment          = this.getFragment();
            var docMode           = document.documentMode;
            var oldIE             = (isExplorer.exec(navigator.userAgent.toLowerCase()) && (!docMode || docMode <= 7));

            // Normalize root to always include a leading and trailing slash.
            this.root = ('/' + this.root + '/').replace(rootStripper, '/');

            if (oldIE && this._wantsHashChange) {
                var frame = Backbone.$('<iframe src="javascript:0" tabindex="-1">');
                this.iframe = frame.hide().appendTo('body')[0].contentWindow;
                this.navigate(fragment);
            }

            // Depending on whether we're using pushState or hashes, and whether
            // 'onhashchange' is supported, determine how we check the URL state.
            if (this._hasPushState) {
                Backbone.$(window).on('popstate', this.checkUrl);
            } else if (this._wantsHashChange && ('onhashchange' in window) && !oldIE) {
                Backbone.$(window).on('hashchange', this.checkUrl);
            } else if (this._wantsHashChange) {
                this._checkUrlInterval = setInterval(this.checkUrl, this.interval);
            }

            // Determine if we need to change the base url, for a pushState link
            // opened by a non-pushState browser.
            this.fragment = fragment;
            var loc = this.location;

            // 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()) {
                    this.fragment = this.getFragment(null, true);
                    this.location.replace(this.root + '#' + this.fragment);
                    // 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() && loc.hash) {
                    this.fragment = this.getHash().replace(routeStripper, '');
                    this.history.replaceState({}, document.title, this.root + this.fragment);
                }

            }

            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() {
            Backbone.$(window).off('popstate', this.checkUrl).off('hashchange', this.checkUrl);
            // 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 (current === this.fragment && this.iframe) {
                current = this.getFragment(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) {
            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};

            var url = this.root + (fragment = this.getFragment(fragment || ''));

            // Strip the hash for matching.
            fragment = fragment.replace(pathStripper, '');

            if (this.fragment === fragment) return;
            this.fragment = fragment;

            // Don't include a trailing slash on the root.
            if (fragment === '' && url !== '/') url = url.slice(0, -1);

            // If pushState is available, we use it to set the fragment as a real URL.
            if (this._hasPushState) {
                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.getFragment(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's 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.
        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(model, resp, options);
            model.trigger('error', model, resp, options);
        };
    };

    return Backbone;

}));