Index: src/wp-includes/js/backbone.js
===================================================================
--- src/wp-includes/js/backbone.js	(revision 36320)
+++ src/wp-includes/js/backbone.js	(working copy)
@@ -1,12 +1,17 @@
-//     Backbone.js 1.1.2
+//     Backbone.js 1.2.3
 
-//     (c) 2010-2014 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
+//     (c) 2010-2015 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 //     Backbone may be freely distributed under the MIT license.
 //     For all details and documentation:
 //     http://backbonejs.org
 
-(function(root, factory) {
+(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) {
@@ -17,8 +22,9 @@
 
   // 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, _);
+    var _ = require('underscore'), $;
+    try { $ = require('jquery'); } catch(e) {}
+    factory(root, exports, _, $);
 
   // Finally, as a browser global.
   } else {
@@ -25,7 +31,7 @@
     root.Backbone = factory(root, {}, root._, (root.jQuery || root.Zepto || root.ender || root.$));
   }
 
-}(this, function(root, Backbone, _, $) {
+}(function(root, Backbone, _, $) {
 
   // Initial Setup
   // -------------
@@ -34,14 +40,11 @@
   // 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;
+  // 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 = '1.1.2';
+  Backbone.VERSION = '1.2.3';
 
   // For Backbone's purposes, jQuery, Zepto, Ender, or My Library (kidding) owns
   // the `$` variable.
@@ -60,17 +63,65 @@
   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/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
-  // custom events. You may bind with `on` or remove with `off` callback
-  // functions to an event; `trigger`-ing an event fires all callbacks in
+  // 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 = {};
@@ -78,125 +129,236 @@
   //     object.on('expand', function(){ alert('expanded'); });
   //     object.trigger('expand');
   //
-  var Events = Backbone.Events = {
+  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;
-    },
+  // Regular expression used to split event strings.
+  var eventSplitter = /\s+/;
 
-    // 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;
+  // 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);
       }
-      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];
-        }
+    } 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;
+  };
 
-      return this;
-    },
+  // 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);
+  };
 
-    // 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;
-    },
+  // 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
+    });
 
-    // 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;
+    if (listening) {
+      var listeners = obj._listeners || (obj._listeners = {});
+      listeners[listening.id] = listening;
     }
 
+    return obj;
   };
 
-  // Regular expression used to split event strings.
-  var eventSplitter = /\s+/;
+  // 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];
 
-  // 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;
+    // 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};
+    }
 
-    // Handle event maps.
-    if (typeof name === 'object') {
-      for (var key in name) {
-        obj[action].apply(obj, [key, name[key]].concat(rest));
+    // Bind callbacks on obj, and keep track of them on listening.
+    internalOn(obj, name, callback, this, listening);
+    return this;
+  };
+
+  // The reducing API that adds a callback to the `events` object.
+  var onApi = function(events, name, callback, options) {
+    if (callback) {
+      var handlers = events[name] || (events[name] = []);
+      var context = options.context, ctx = options.ctx, listening = options.listening;
+      if (listening) listening.count++;
+
+      handlers.push({ callback: callback, context: context, ctx: context || ctx, listening: listening });
+    }
+    return events;
+  };
+
+  // Remove one or many callbacks. If `context` is null, removes all
+  // callbacks with that function. If `callback` is null, removes all
+  // callbacks for the event. If `name` is null, removes all bound
+  // callbacks for all events.
+  Events.off =  function(name, callback, context) {
+    if (!this._events) return this;
+    this._events = eventsApi(offApi, this._events, name, callback, {
+        context: context,
+        listeners: this._listeners
+    });
+    return this;
+  };
+
+  // Tell this object to stop listening to either specific events ... or
+  // to every object it's currently listening to.
+  Events.stopListening =  function(obj, name, callback) {
+    var listeningTo = this._listeningTo;
+    if (!listeningTo) return this;
+
+    var ids = obj ? [obj._listenId] : _.keys(listeningTo);
+
+    for (var i = 0; i < ids.length; i++) {
+      var listening = listeningTo[ids[i]];
+
+      // If listening doesn't exist, this object is not currently
+      // listening to obj. Break out early.
+      if (!listening) break;
+
+      listening.obj.off(name, callback, this);
+    }
+    if (_.isEmpty(listeningTo)) this._listeningTo = void 0;
+
+    return this;
+  };
+
+  // The reducing API that removes a callback from the `events` object.
+  var offApi = function(events, name, callback, options) {
+    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 false;
+      return;
     }
 
-    // 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));
+    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];
+          }
+        }
       }
-      return false;
+
+      // Update tail event if the list has any events.  Otherwise, clean up.
+      if (remaining.length) {
+        events[name] = remaining;
+      } else {
+        delete events[name];
+      }
     }
+    if (_.size(events)) return events;
+  };
 
-    return true;
+  // 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));
+    return this.on(events, void 0, context);
   };
 
+  // Inversion-of-control versions of `once`.
+  Events.listenToOnce =  function(obj, name, callback) {
+    // Map the event into a `{event: once}` object.
+    var events = eventsApi(onceMap, {}, name, callback, _.bind(this.stopListening, this, obj));
+    return this.listenTo(obj, events);
+  };
+
+  // Reduces the event callbacks into a map of `{event: onceWrapper}`.
+  // `offer` unbinds the `onceWrapper` after it 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, cb, args) {
+    if (objEvents) {
+      var events = objEvents[name];
+      var allEvents = objEvents.all;
+      if (events && allEvents) allEvents = allEvents.slice();
+      if (events) triggerEvents(events, args);
+      if (allEvents) triggerEvents(allEvents, [name].concat(args));
+    }
+    return objEvents;
+  };
+
   // A difficult-to-believe, but optimized internal dispatch function for
   // triggering events. Tries to keep the usual cases speedy (most internal
   // Backbone events have 3 arguments).
@@ -211,22 +373,6 @@
     }
   };
 
-  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;
@@ -248,7 +394,7 @@
   var Model = Backbone.Model = function(attributes, options) {
     var attrs = attributes || {};
     options || (options = {});
-    this.cid = _.uniqueId('c');
+    this.cid = _.uniqueId(this.cidPrefix);
     this.attributes = {};
     if (options.collection) this.collection = options.collection;
     if (options.parse) attrs = this.parse(attrs, options) || {};
@@ -271,6 +417,10 @@
     // 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(){},
@@ -302,14 +452,19 @@
       return this.get(attr) != null;
     },
 
+    // Special-cased proxy to underscore's `_.matches` method.
+    matches: function(attrs) {
+      return !!_.iteratee(attrs, this)(this.attributes);
+    },
+
     // Set a hash of model attributes on the object, firing `"change"`. This is
     // the core primitive operation of a model, updating the data and notifying
     // anyone who needs to know about the change in state. The heart of the beast.
     set: function(key, val, options) {
-      var attr, attrs, unset, changes, silent, changing, prev, current;
       if (key == null) return this;
 
       // Handle both `"key", value` and `{key: value}` -style arguments.
+      var attrs;
       if (typeof key === 'object') {
         attrs = key;
         options = val;
@@ -323,37 +478,40 @@
       if (!this._validate(attrs, options)) return false;
 
       // Extract attributes and options.
-      unset           = options.unset;
-      silent          = options.silent;
-      changes         = [];
-      changing        = this._changing;
-      this._changing  = true;
+      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 = {};
       }
-      current = this.attributes, prev = this._previousAttributes;
 
-      // Check for changes of `id`.
-      if (this.idAttribute in attrs) this.id = attrs[this.idAttribute];
+      var current = this.attributes;
+      var changed = this.changed;
+      var prev    = this._previousAttributes;
 
       // For each `set` attribute, update or delete the current value.
-      for (attr in attrs) {
+      for (var attr in attrs) {
         val = attrs[attr];
         if (!_.isEqual(current[attr], val)) changes.push(attr);
         if (!_.isEqual(prev[attr], val)) {
-          this.changed[attr] = val;
+          changed[attr] = val;
         } else {
-          delete this.changed[attr];
+          delete changed[attr];
         }
         unset ? delete current[attr] : current[attr] = val;
       }
 
+      // Update the `id`.
+      this.id = this.get(this.idAttribute);
+
       // Trigger all relevant attribute changes.
       if (!silent) {
         if (changes.length) this._pending = options;
-        for (var i = 0, l = changes.length; i < l; i++) {
+        for (var i = 0; i < changes.length; i++) {
           this.trigger('change:' + changes[i], this, current[changes[i]], options);
         }
       }
@@ -401,13 +559,14 @@
     // 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;
+      var changed = {};
       for (var attr in diff) {
-        if (_.isEqual(old[attr], (val = diff[attr]))) continue;
-        (changed || (changed = {}))[attr] = val;
+        var val = diff[attr];
+        if (_.isEqual(old[attr], val)) continue;
+        changed[attr] = val;
       }
-      return changed;
+      return _.size(changed) ? changed : false;
     },
 
     // Get the previous value of an attribute, recorded at the time the last
@@ -423,17 +582,16 @@
       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 the model from the server, merging the response with the model's
+    // local attributes. Any changed attributes will trigger a "change" event.
     fetch: function(options) {
-      options = options ? _.clone(options) : {};
-      if (options.parse === void 0) options.parse = true;
+      options = _.extend({parse: true}, options);
       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);
+        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);
@@ -444,9 +602,8 @@
     // 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.
+      var attrs;
       if (key == null || typeof key === 'object') {
         attrs = key;
         options = val;
@@ -454,46 +611,43 @@
         (attrs = {})[key] = val;
       }
 
-      options = _.extend({validate: true}, options);
+      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 && !options.wait) {
+      if (attrs && !wait) {
         if (!this.set(attrs, options)) return false;
       } else {
         if (!this._validate(attrs, options)) return false;
       }
 
-      // Set temporary attributes if `{wait: true}`.
-      if (attrs && 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;
+      var attributes = this.attributes;
       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);
+        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);
 
-      method = this.isNew() ? 'create' : (options.patch ? 'patch' : 'update');
-      if (method === 'patch') options.attrs = attrs;
-      xhr = this.sync(method, 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.
-      if (attrs && options.wait) this.attributes = attributes;
+      this.attributes = attributes;
 
       return xhr;
     },
@@ -505,25 +659,27 @@
       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 (options.wait || model.isNew()) destroy();
-        if (success) success(model, resp, options);
+        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()) {
-        options.success();
-        return false;
+        _.defer(options.success);
+      } else {
+        wrapError(this, options);
+        xhr = this.sync('delete', this, options);
       }
-      wrapError(this, options);
-
-      var xhr = this.sync('delete', this, options);
-      if (!options.wait) destroy();
+      if (!wait) destroy();
       return xhr;
     },
 
@@ -536,7 +692,8 @@
         _.result(this.collection, 'url') ||
         urlError();
       if (this.isNew()) return base;
-      return base.replace(/([^\/])$/, '$1/') + encodeURIComponent(this.id);
+      var id = this.get(this.idAttribute);
+      return base.replace(/[^\/]$/, '$&/') + encodeURIComponent(id);
     },
 
     // **parse** converts a response into the hash of attributes to be `set` on
@@ -557,7 +714,7 @@
 
     // Check if the model is currently in a valid state.
     isValid: function(options) {
-      return this._validate({}, _.extend(options || {}, { validate: true }));
+      return this._validate({}, _.defaults({validate: true}, options));
     },
 
     // Run validation against the next complete set of model attributes,
@@ -573,23 +730,19 @@
 
   });
 
-  // Underscore methods that we want to implement on the Model.
-  var modelMethods = ['keys', 'values', 'pairs', 'invert', 'pick', 'omit'];
+  // 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`.
-  _.each(modelMethods, function(method) {
-    Model.prototype[method] = function() {
-      var args = slice.call(arguments);
-      args.unshift(this.attributes);
-      return _[method].apply(_, args);
-    };
-  });
+  addUnderscoreMethods(Model, modelMethods, 'attributes');
 
   // 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
+  // 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
@@ -611,6 +764,16 @@
   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;
+    for (var 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, {
 
@@ -625,7 +788,7 @@
     // 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); });
+      return this.map(function(model) { return model.toJSON(options); });
     },
 
     // Proxy `Backbone.sync` by default.
@@ -633,7 +796,9 @@
       return Backbone.sync.apply(this, arguments);
     },
 
-    // Add a model, or list of models to the set.
+    // 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));
     },
@@ -640,25 +805,12 @@
 
     // 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] : _.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;
+      var removed = this._removeModels(models, options);
+      if (!options.silent && 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,
@@ -666,78 +818,88 @@
     // 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 = _.defaults({}, options, setOptions);
-      if (options.parse) models = this.parse(models, options);
+      if (options.parse && !this._isModel(models)) models = this.parse(models, options);
+
       var singular = !_.isArray(models);
-      models = singular ? (models ? [models] : []) : _.clone(models);
-      var i, l, id, model, attrs, existing, sort;
+      models = singular ? [models] : models.slice();
+
       var at = options.at;
-      var targetModel = this.model;
+      if (at != null) at = +at;
+      if (at < 0) at += this.length + 1;
+
+      var set = [];
+      var toAdd = [];
+      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;
-      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'];
-        }
+      var model;
+      for (var 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.
-        if (existing = this.get(id)) {
-          if (remove) modelMap[existing.cid] = true;
-          if (merge) {
-            attrs = attrs === model ? model.attributes : attrs;
+        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);
-            if (sortable && !sort && existing.hasChanged(sortAttr)) sort = true;
+            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(attrs, options);
-          if (!model) continue;
-          toAdd.push(model);
-          this._addReference(model, options);
+          model = models[i] = this._prepareModel(model, options);
+          if (model) {
+            toAdd.push(model);
+            this._addReference(model, options);
+            modelMap[model.cid] = true;
+            set.push(model);
+          }
         }
-
-        // 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.
+      // Remove stale models.
       if (remove) {
-        for (i = 0, l = this.length; i < l; ++i) {
-          if (!modelMap[(model = this.models[i]).cid]) toRemove.push(model);
+        for (i = 0; i < this.length; i++) {
+          model = this.models[i];
+          if (!modelMap[model.cid]) toRemove.push(model);
         }
-        if (toRemove.length) this.remove(toRemove, options);
+        if (toRemove.length) this._removeModels(toRemove, options);
       }
 
       // See if sorting is needed, update `length` and splice in new models.
-      if (toAdd.length || (order && order.length)) {
+      var orderChanged = false;
+      var replace = !sortable && add && remove;
+      if (set.length && replace) {
+        orderChanged = this.length != set.length || _.some(this.models, function(model, index) {
+          return model !== set[index];
+        });
+        this.models.length = 0;
+        splice(this.models, set, 0);
+        this.length = this.models.length;
+      } else if (toAdd.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]);
-          }
-        }
+        splice(this.models, toAdd, at == null ? this.length : at);
+        this.length = this.models.length;
       }
 
       // Silently sort the collection if appropriate.
@@ -745,10 +907,13 @@
 
       // 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);
+        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 || (order && order.length)) this.trigger('sort', this, options);
+        if (sort || orderChanged) this.trigger('sort', this, options);
+        if (toAdd.length || toRemove.length) this.trigger('update', this, options);
       }
 
       // Return the added (or merged) model (or models).
@@ -760,8 +925,8 @@
     // 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++) {
+      options = options ? _.clone(options) : {};
+      for (var i = 0; i < this.models.length; i++) {
         this._removeReference(this.models[i], options);
       }
       options.previousModels = this.models;
@@ -779,8 +944,7 @@
     // 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;
+      return this.remove(model, options);
     },
 
     // Add a model to the beginning of the collection.
@@ -791,8 +955,7 @@
     // Remove a model from the beginning of the collection.
     shift: function(options) {
       var model = this.at(0);
-      this.remove(model, options);
-      return model;
+      return this.remove(model, options);
     },
 
     // Slice out a sub-array of models from the collection.
@@ -803,11 +966,13 @@
     // 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];
+      var id = this.modelId(this._isModel(obj) ? obj.attributes : obj);
+      return this._byId[obj] || this._byId[id] || this._byId[obj.cid];
     },
 
     // Get the model at the given index.
     at: function(index) {
+      if (index < 0) index += this.length;
       return this.models[index];
     },
 
@@ -814,13 +979,7 @@
     // 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 this[first ? 'find' : 'filter'](attrs);
     },
 
     // Return the first model with matching attributes. Useful for simple cases
@@ -833,16 +992,19 @@
     // 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');
+      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 (_.isString(this.comparator) || this.comparator.length === 1) {
-        this.models = this.sortBy(this.comparator, this);
+      if (length === 1 || _.isString(comparator)) {
+        this.models = this.sortBy(comparator);
       } else {
-        this.models.sort(_.bind(this.comparator, this));
+        this.models.sort(comparator);
       }
-
       if (!options.silent) this.trigger('sort', this, options);
       return this;
     },
@@ -856,14 +1018,13 @@
     // 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;
+      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(collection, resp, options);
+        if (success) success.call(options.context, collection, resp, options);
         collection.trigger('sync', collection, resp, options);
       };
       wrapError(this, options);
@@ -875,13 +1036,15 @@
     // 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 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(model, resp) {
-        if (options.wait) collection.add(model, options);
-        if (success) success(model, resp, options);
+      options.success = function(model, resp, callbackOpts) {
+        if (wait) collection.add(model, callbackOpts);
+        if (success) success.call(callbackOpts.context, model, resp, callbackOpts);
       };
       model.save(null, options);
       return model;
@@ -895,9 +1058,17 @@
 
     // Create a new collection with an identical list of models as this one.
     clone: function() {
-      return new this.constructor(this.models);
+      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() {
@@ -909,7 +1080,10 @@
     // Prepare a hash of attributes (or other model) to be added to this
     // collection.
     _prepareModel: function(attrs, options) {
-      if (attrs instanceof Model) return attrs;
+      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);
@@ -918,16 +1092,47 @@
       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--;
+
+        if (!options.silent) {
+          options.index = index;
+          model.trigger('remove', model, this, options);
+        }
+
+        removed.push(model);
+        this._removeReference(model, options);
+      }
+      return removed.length ? removed : false;
+    },
+
+    // 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;
-      if (model.id != null) this._byId[model.id] = model;
-      if (!model.collection) model.collection = this;
+      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);
     },
@@ -939,9 +1144,13 @@
     _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;
+      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);
     }
@@ -951,35 +1160,18 @@
   // 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'];
+  var collectionMethods = { forEach: 3, each: 3, map: 3, collect: 3, reduce: 4,
+      foldl: 4, inject: 4, reduceRight: 4, foldr: 4, find: 3, detect: 3, filter: 3,
+      select: 3, reject: 3, every: 3, all: 3, some: 3, any: 3, include: 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};
 
   // 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);
-    };
-  });
+  addUnderscoreMethods(Collection, collectionMethods, 'models');
 
-  // Underscore methods that take a property name as an argument.
-  var attributeMethods = ['groupBy', 'countBy', 'sortBy', 'indexBy'];
-
-  // Use attributes instead of properties.
-  _.each(attributeMethods, function(method) {
-    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
   // -------------
 
@@ -995,17 +1187,15 @@
   // 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.
+  // 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.
@@ -1034,21 +1224,37 @@
     // Remove this view by taking the element out of the DOM, and removing any
     // applicable Backbone.Events listeners.
     remove: function() {
-      this.$el.remove();
+      this._removeElement();
       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();
+    // 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"}*
@@ -1062,37 +1268,49 @@
     // 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;
+      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[events[key]];
+        if (!_.isFunction(method)) method = this[method];
         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);
-        }
+        this.delegate(match[1], match[2], _.bind(method, this));
       }
       return this;
     },
 
-    // Clears all callbacks previously bound to the view with `delegateEvents`.
+    // 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.$el.on(eventName + '.delegateEvents' + this.cid, selector, listener);
+      return this;
+    },
+
+    // Clears all callbacks previously bound to the view by `delegateEvents`.
     // You usually don't need to use this, but may wish to if you have multiple
     // Backbone views attached to the same DOM element.
     undelegateEvents: function() {
-      this.$el.off('.delegateEvents' + this.cid);
+      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
@@ -1102,11 +1320,17 @@
         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($el, false);
+        this.setElement(this._createElement(_.result(this, 'tagName')));
+        this._setAttributes(attrs);
       } else {
-        this.setElement(_.result(this, 'el'), false);
+        this.setElement(_.result(this, 'el'));
       }
+    },
+
+    // Set attributes from a hash on this view's element.  Exposed for
+    // subclasses using an alternative DOM manipulation API.
+    _setAttributes: function(attributes) {
+      this.$el.attr(attributes);
     }
 
   });
@@ -1175,14 +1399,13 @@
       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");
-      };
-    }
+    // 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));
@@ -1190,10 +1413,6 @@
     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',
@@ -1251,10 +1470,11 @@
       var router = this;
       Backbone.history.route(route, function(fragment) {
         var args = router._extractParameters(route, fragment);
-        router.execute(callback, args);
-        router.trigger.apply(router, ['route:' + name].concat(args));
-        router.trigger('route', name, args);
-        Backbone.history.trigger('route', router, name, args);
+        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;
     },
@@ -1261,7 +1481,7 @@
 
     // 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) {
+    execute: function(callback, args, name) {
       if (callback) callback.apply(this, args);
     },
 
@@ -1319,7 +1539,7 @@
   // falls back to polling.
   var History = Backbone.History = function() {
     this.handlers = [];
-    _.bindAll(this, 'checkUrl');
+    this.checkUrl = _.bind(this.checkUrl, this);
 
     // Ensure that `History` can be used outside of the browser.
     if (typeof window !== 'undefined') {
@@ -1334,12 +1554,6 @@
   // 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 = /\/$/;
-
   // Cached regex for stripping urls of hash.
   var pathStripper = /#.*$/;
 
@@ -1355,9 +1569,31 @@
 
     // Are we at the app root?
     atRoot: function() {
-      return this.location.pathname.replace(/[^\/]$/, '$&/') === this.root;
+      var path = this.location.pathname.replace(/[^\/]$/, '$&/');
+      return path === this.root && !this.getSearch();
     },
 
+    // Does the pathname match the root?
+    matchRoot: function() {
+      var path = this.decodeFragment(this.location.pathname);
+      var root = path.slice(0, this.root.length - 1) + '/';
+      return root === this.root;
+    },
+
+    // Unicode characters in `location.pathname` are percent encoded so they're
+    // decoded for comparison. `%25` should not be decoded since it may be part
+    // of an encoded parameter.
+    decodeFragment: function(fragment) {
+      return decodeURI(fragment.replace(/%25/g, '%2525'));
+    },
+
+    // In IE6, the hash fragment and search params are incorrect if the
+    // fragment contains `?`.
+    getSearch: function() {
+      var match = this.location.href.replace(/#.*/, '').match(/\?.+/);
+      return match ? match[0] : '';
+    },
+
     // Gets the true hash value. Cannot use location.hash directly due to bug
     // in Firefox where location.hash will always be decoded.
     getHash: function(window) {
@@ -1365,14 +1601,19 @@
       return match ? match[1] : '';
     },
 
-    // Get the cross-browser normalized URL fragment, either from the URL,
-    // the hash, or the override.
-    getFragment: function(fragment, forcePushState) {
+    // 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._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);
+        if (this._usePushState || !this._wantsHashChange) {
+          fragment = this.getPath();
         } else {
           fragment = this.getHash();
         }
@@ -1383,7 +1624,7 @@
     // 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");
+      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?
@@ -1391,36 +1632,16 @@
       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.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));
+      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, '/');
 
-      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) {
@@ -1428,20 +1649,50 @@
         // 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);
+          var root = this.root.slice(0, -1) || '/';
+          this.location.replace(root + '#' + this.getPath());
           // Return immediately as browser will do redirect to new url
           return true;
 
         // Or if we've started out with a hash-based route, but we're currently
         // in a browser where it could be `pushState`-based instead...
-        } else if (this._hasPushState && this.atRoot() && loc.hash) {
-          this.fragment = this.getHash().replace(routeStripper, '');
-          this.history.replaceState({}, document.title, this.root + this.fragment);
+        } 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.
+      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();
     },
 
@@ -1448,7 +1699,25 @@
     // 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);
+      // 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;
     },
@@ -1463,9 +1732,13 @@
     // calls `loadUrl`, normalizing across the hidden iframe.
     checkUrl: function(e) {
       var current = this.getFragment();
+
+      // If the user pressed the back button, the iframe's hash will have
+      // changed and we should use that for comparison.
       if (current === this.fragment && this.iframe) {
-        current = this.getFragment(this.getHash(this.iframe));
+        current = this.getHash(this.iframe.contentWindow);
       }
+
       if (current === this.fragment) return false;
       if (this.iframe) this.navigate(current);
       this.loadUrl();
@@ -1475,8 +1748,10 @@
     // match, returns `true`. If no defined routes matches the fragment,
     // returns `false`.
     loadUrl: function(fragment) {
+      // If the root doesn't match, no routes can match either.
+      if (!this.matchRoot()) return false;
       fragment = this.fragment = this.getFragment(fragment);
-      return _.any(this.handlers, function(handler) {
+      return _.some(this.handlers, function(handler) {
         if (handler.route.test(fragment)) {
           handler.callback(fragment);
           return true;
@@ -1495,19 +1770,24 @@
       if (!History.started) return false;
       if (!options || options === true) options = {trigger: !!options};
 
-      var url = this.root + (fragment = this.getFragment(fragment || ''));
+      // Normalize the fragment.
+      fragment = this.getFragment(fragment || '');
 
-      // Strip the hash for matching.
-      fragment = fragment.replace(pathStripper, '');
+      // Don't include a trailing slash on the root.
+      var root = this.root;
+      if (fragment === '' || fragment.charAt(0) === '?') {
+        root = root.slice(0, -1) || '/';
+      }
+      var url = root + fragment;
 
+      // Strip the hash and decode for matching.
+      fragment = this.decodeFragment(fragment.replace(pathStripper, ''));
+
       if (this.fragment === fragment) return;
       this.fragment = fragment;
 
-      // 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) {
+      if (this._usePushState) {
         this.history[options.replace ? 'replaceState' : 'pushState']({}, document.title, url);
 
       // If hash changes haven't been explicitly disabled, update the hash
@@ -1514,12 +1794,18 @@
       // 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)))) {
+        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) this.iframe.document.open().close();
-          this._updateHash(this.iframe.location, fragment, options.replace);
+          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-
@@ -1550,7 +1836,7 @@
   // Helpers
   // -------
 
-  // Helper function to correctly set up the prototype chain, for subclasses.
+  // 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) {
@@ -1559,7 +1845,7 @@
 
     // 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.
+    // by us to simply call the parent constructor.
     if (protoProps && _.has(protoProps, 'constructor')) {
       child = protoProps.constructor;
     } else {
@@ -1570,7 +1856,7 @@
     _.extend(child, parent, staticProps);
 
     // Set the prototype chain to inherit from `parent`, without calling
-    // `parent`'s constructor function.
+    // `parent` constructor function.
     var Surrogate = function(){ this.constructor = child; };
     Surrogate.prototype = parent.prototype;
     child.prototype = new Surrogate;
@@ -1598,7 +1884,7 @@
   var wrapError = function(model, options) {
     var error = options.error;
     options.error = function(resp) {
-      if (error) error(model, resp, options);
+      if (error) error.call(options.context, model, resp, options);
       model.trigger('error', model, resp, options);
     };
   };
Index: src/wp-includes/js/backbone.min.js
===================================================================
--- src/wp-includes/js/backbone.min.js	(revision 36320)
+++ src/wp-includes/js/backbone.min.js	(working copy)
@@ -1 +1 @@
-(function(t,e){if(typeof define==="function"&&define.amd){define(["underscore","jquery","exports"],function(i,r,s){t.Backbone=e(t,s,i,r)})}else if(typeof exports!=="undefined"){var i=require("underscore");e(t,exports,i)}else{t.Backbone=e(t,{},t._,t.jQuery||t.Zepto||t.ender||t.$)}})(this,function(t,e,i,r){var s=t.Backbone;var n=[];var a=n.push;var o=n.slice;var h=n.splice;e.VERSION="1.1.2";e.$=r;e.noConflict=function(){t.Backbone=s;return this};e.emulateHTTP=false;e.emulateJSON=false;var u=e.Events={on:function(t,e,i){if(!c(this,"on",t,[e,i])||!e)return this;this._events||(this._events={});var r=this._events[t]||(this._events[t]=[]);r.push({callback:e,context:i,ctx:i||this});return this},once:function(t,e,r){if(!c(this,"once",t,[e,r])||!e)return this;var s=this;var n=i.once(function(){s.off(t,n);e.apply(this,arguments)});n._callback=e;return this.on(t,n,r)},off:function(t,e,r){var s,n,a,o,h,u,l,f;if(!this._events||!c(this,"off",t,[e,r]))return this;if(!t&&!e&&!r){this._events=void 0;return this}o=t?[t]:i.keys(this._events);for(h=0,u=o.length;h<u;h++){t=o[h];if(a=this._events[t]){this._events[t]=s=[];if(e||r){for(l=0,f=a.length;l<f;l++){n=a[l];if(e&&e!==n.callback&&e!==n.callback._callback||r&&r!==n.context){s.push(n)}}}if(!s.length)delete this._events[t]}}return this},trigger:function(t){if(!this._events)return this;var e=o.call(arguments,1);if(!c(this,"trigger",t,e))return this;var i=this._events[t];var r=this._events.all;if(i)f(i,e);if(r)f(r,arguments);return this},stopListening:function(t,e,r){var s=this._listeningTo;if(!s)return this;var n=!e&&!r;if(!r&&typeof e==="object")r=this;if(t)(s={})[t._listenId]=t;for(var a in s){t=s[a];t.off(e,r,this);if(n||i.isEmpty(t._events))delete this._listeningTo[a]}return this}};var l=/\s+/;var c=function(t,e,i,r){if(!i)return true;if(typeof i==="object"){for(var s in i){t[e].apply(t,[s,i[s]].concat(r))}return false}if(l.test(i)){var n=i.split(l);for(var a=0,o=n.length;a<o;a++){t[e].apply(t,[n[a]].concat(r))}return 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r=t||{};e||(e={});this.cid=i.uniqueId("c");this.attributes={};if(e.collection)this.collection=e.collection;if(e.parse)r=this.parse(r,e)||{};r=i.defaults({},r,i.result(this,"defaults"));this.set(r,e);this.changed={};this.initialize.apply(this,arguments)};i.extend(p.prototype,u,{changed:null,validationError:null,idAttribute:"id",initialize:function(){},toJSON:function(t){return i.clone(this.attributes)},sync:function(){return e.sync.apply(this,arguments)},get:function(t){return this.attributes[t]},escape:function(t){return i.escape(this.get(t))},has:function(t){return this.get(t)!=null},set:function(t,e,r){var s,n,a,o,h,u,l,c;if(t==null)return this;if(typeof t==="object"){n=t;r=e}else{(n={})[t]=e}r||(r={});if(!this._validate(n,r))return false;a=r.unset;h=r.silent;o=[];u=this._changing;this._changing=true;if(!u){this._previousAttributes=i.clone(this.attributes);this.changed={}}c=this.attributes,l=this._previousAttributes;if(this.idAttribute in n)this.id=n[this.idAttribute];for(s in 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false}if(u)u(h,t,r);h.trigger("sync",h,t,r)};q(this,r);n=this.isNew()?"create":r.patch?"patch":"update";if(n==="patch")r.attrs=s;a=this.sync(n,this,r);if(s&&r.wait)this.attributes=o;return a},destroy:function(t){t=t?i.clone(t):{};var e=this;var r=t.success;var s=function(){e.trigger("destroy",e,e.collection,t)};t.success=function(i){if(t.wait||e.isNew())s();if(r)r(e,i,t);if(!e.isNew())e.trigger("sync",e,i,t)};if(this.isNew()){t.success();return false}q(this,t);var n=this.sync("delete",this,t);if(!t.wait)s();return n},url:function(){var t=i.result(this,"urlRoot")||i.result(this.collection,"url")||M();if(this.isNew())return t;return t.replace(/([^\/])$/,"$1/")+encodeURIComponent(this.id)},parse:function(t,e){return t},clone:function(){return new this.constructor(this.attributes)},isNew:function(){return!this.has(this.idAttribute)},isValid:function(t){return this._validate({},i.extend(t||{},{validate:true}))},_validate:function(t,e){if(!e.validate||!this.validate)return true;t=i.extend({},this.attributes,t);var r=this.validationError=this.validate(t,e)||null;if(!r)return true;this.trigger("invalid",this,r,i.extend(e,{validationError:r}));return false}});var v=["keys","values","pairs","invert","pick","omit"];i.each(v,function(t){p.prototype[t]=function(){var e=o.call(arguments);e.unshift(this.attributes);return i[t].apply(i,e)}});var g=e.Collection=function(t,e){e||(e={});if(e.model)this.model=e.model;if(e.comparator!==void 0)this.comparator=e.comparator;this._reset();this.initialize.apply(this,arguments);if(t)this.reset(t,i.extend({silent:true},e))};var m={add:true,remove:true,merge:true};var y={add:true,remove:false};i.extend(g.prototype,u,{model:p,initialize:function(){},toJSON:function(t){return this.map(function(e){return e.toJSON(t)})},sync:function(){return e.sync.apply(this,arguments)},add:function(t,e){return this.set(t,i.extend({merge:false},e,y))},remove:function(t,e){var r=!i.isArray(t);t=r?[t]:i.clone(t);e||(e={});var s,n,a,o;for(s=0,n=t.length;s<n;s++){o=t[s]=this.get(t[s]);if(!o)continue;delete this._byId[o.id];delete this._byId[o.cid];a=this.indexOf(o);this.models.splice(a,1);this.length--;if(!e.silent){e.index=a;o.trigger("remove",o,this,e)}this._removeReference(o,e)}return r?t[0]:t},set:function(t,e){e=i.defaults({},e,m);if(e.parse)t=this.parse(t,e);var r=!i.isArray(t);t=r?t?[t]:[]:i.clone(t);var s,n,a,o,h,u,l;var c=e.at;var f=this.model;var d=this.comparator&&c==null&&e.sort!==false;var v=i.isString(this.comparator)?this.comparator:null;var g=[],y=[],_={};var b=e.add,w=e.merge,x=e.remove;var E=!d&&b&&x?[]:false;for(s=0,n=t.length;s<n;s++){h=t[s]||{};if(h instanceof p){a=o=h}else{a=h[f.prototype.idAttribute||"id"]}if(u=this.get(a)){if(x)_[u.cid]=true;if(w){h=h===o?o.attributes:h;if(e.parse)h=u.parse(h,e);u.set(h,e);if(d&&!l&&u.hasChanged(v))l=true}t[s]=u}else 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e=this.at(this.length-1);this.remove(e,t);return e},unshift:function(t,e){return this.add(t,i.extend({at:0},e))},shift:function(t){var e=this.at(0);this.remove(e,t);return e},slice:function(){return o.apply(this.models,arguments)},get:function(t){if(t==null)return void 0;return this._byId[t]||this._byId[t.id]||this._byId[t.cid]},at:function(t){return this.models[t]},where:function(t,e){if(i.isEmpty(t))return e?void 0:[];return this[e?"find":"filter"](function(e){for(var i in t){if(t[i]!==e.get(i))return false}return true})},findWhere:function(t){return this.where(t,true)},sort:function(t){if(!this.comparator)throw new Error("Cannot sort a set without a comparator");t||(t={});if(i.isString(this.comparator)||this.comparator.length===1){this.models=this.sortBy(this.comparator,this)}else{this.models.sort(i.bind(this.comparator,this))}if(!t.silent)this.trigger("sort",this,t);return this},pluck:function(t){return i.invoke(this.models,"get",t)},fetch:function(t){t=t?i.clone(t):{};if(t.parse===void 0)t.parse=true;var e=t.success;var r=this;t.success=function(i){var s=t.reset?"reset":"set";r[s](i,t);if(e)e(r,i,t);r.trigger("sync",r,i,t)};q(this,t);return this.sync("read",this,t)},create:function(t,e){e=e?i.clone(e):{};if(!(t=this._prepareModel(t,e)))return false;if(!e.wait)this.add(t,e);var r=this;var s=e.success;e.success=function(t,i){if(e.wait)r.add(t,e);if(s)s(t,i,e)};t.save(null,e);return t},parse:function(t,e){return t},clone:function(){return new this.constructor(this.models)},_reset:function(){this.length=0;this.models=[];this._byId={}},_prepareModel:function(t,e){if(t instanceof p)return t;e=e?i.clone(e):{};e.collection=this;var r=new this.model(t,e);if(!r.validationError)return r;this.trigger("invalid",this,r.validationError,e);return false},_addReference:function(t,e){this._byId[t.cid]=t;if(t.id!=null)this._byId[t.id]=t;if(!t.collection)t.collection=this;t.on("all",this._onModelEvent,this)},_removeReference:function(t,e){if(this===t.collection)delete t.collection;t.off("all",this._onModelEvent,this)},_onModelEvent:function(t,e,i,r){if((t==="add"||t==="remove")&&i!==this)return;if(t==="destroy")this.remove(e,r);if(e&&t==="change:"+e.idAttribute){delete this._byId[e.previous(e.idAttribute)];if(e.id!=null)this._byId[e.id]=e}this.trigger.apply(this,arguments)}});var _=["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"];i.each(_,function(t){g.prototype[t]=function(){var e=o.call(arguments);e.unshift(this.models);return i[t].apply(i,e)}});var b=["groupBy","countBy","sortBy","indexBy"];i.each(b,function(t){g.prototype[t]=function(e,r){var s=i.isFunction(e)?e:function(t){return t.get(e)};return i[t](this.models,s,r)}});var w=e.View=function(t){this.cid=i.uniqueId("view");t||(t={});i.extend(this,i.pick(t,E));this._ensureElement();this.initialize.apply(this,arguments);this.delegateEvents()};var x=/^(\S+)\s*(.*)$/;var E=["model","collection","el","id","attributes","className","tagName","events"];i.extend(w.prototype,u,{tagName:"div",$:function(t){return this.$el.find(t)},initialize:function(){},render:function(){return this},remove:function(){this.$el.remove();this.stopListening();return this},setElement:function(t,i){if(this.$el)this.undelegateEvents();this.$el=t instanceof e.$?t:e.$(t);this.el=this.$el[0];if(i!==false)this.delegateEvents();return this},delegateEvents:function(t){if(!(t||(t=i.result(this,"events"))))return this;this.undelegateEvents();for(var e in t){var r=t[e];if(!i.isFunction(r))r=this[t[e]];if(!r)continue;var s=e.match(x);var n=s[1],a=s[2];r=i.bind(r,this);n+=".delegateEvents"+this.cid;if(a===""){this.$el.on(n,r)}else{this.$el.on(n,a,r)}}return this},undelegateEvents:function(){this.$el.off(".delegateEvents"+this.cid);return this},_ensureElement:function(){if(!this.el){var t=i.extend({},i.result(this,"attributes"));if(this.id)t.id=i.result(this,"id");if(this.className)t["class"]=i.result(this,"className");var r=e.$("<"+i.result(this,"tagName")+">").attr(t);this.setElement(r,false)}else{this.setElement(i.result(this,"el"),false)}}});e.sync=function(t,r,s){var n=T[t];i.defaults(s||(s={}),{emulateHTTP:e.emulateHTTP,emulateJSON:e.emulateJSON});var a={type:n,dataType:"json"};if(!s.url){a.url=i.result(r,"url")||M()}if(s.data==null&&r&&(t==="create"||t==="update"||t==="patch")){a.contentType="application/json";a.data=JSON.stringify(s.attrs||r.toJSON(s))}if(s.emulateJSON){a.contentType="application/x-www-form-urlencoded";a.data=a.data?{model:a.data}:{}}if(s.emulateHTTP&&(n==="PUT"||n==="DELETE"||n==="PATCH")){a.type="POST";if(s.emulateJSON)a.data._method=n;var o=s.beforeSend;s.beforeSend=function(t){t.setRequestHeader("X-HTTP-Method-Override",n);if(o)return o.apply(this,arguments)}}if(a.type!=="GET"&&!s.emulateJSON){a.processData=false}if(a.type==="PATCH"&&k){a.xhr=function(){return new ActiveXObject("Microsoft.XMLHTTP")}}var h=s.xhr=e.ajax(i.extend(a,s));r.trigger("request",r,h,s);return h};var k=typeof window!=="undefined"&&!!window.ActiveXObject&&!(window.XMLHttpRequest&&(new XMLHttpRequest).dispatchEvent);var T={create:"POST",update:"PUT",patch:"PATCH","delete":"DELETE",read:"GET"};e.ajax=function(){return e.$.ajax.apply(e.$,arguments)};var $=e.Router=function(t){t||(t={});if(t.routes)this.routes=t.routes;this._bindRoutes();this.initialize.apply(this,arguments)};var S=/\((.*?)\)/g;var H=/(\(\?)?:\w+/g;var A=/\*\w+/g;var I=/[\-{}\[\]+?.,\\\^$|#\s]/g;i.extend($.prototype,u,{initialize:function(){},route:function(t,r,s){if(!i.isRegExp(t))t=this._routeToRegExp(t);if(i.isFunction(r)){s=r;r=""}if(!s)s=this[r];var n=this;e.history.route(t,function(i){var a=n._extractParameters(t,i);n.execute(s,a);n.trigger.apply(n,["route:"+r].concat(a));n.trigger("route",r,a);e.history.trigger("route",n,r,a)});return this},execute:function(t,e){if(t)t.apply(this,e)},navigate:function(t,i){e.history.navigate(t,i);return this},_bindRoutes:function(){if(!this.routes)return;this.routes=i.result(this,"routes");var t,e=i.keys(this.routes);while((t=e.pop())!=null){this.route(t,this.routes[t])}},_routeToRegExp:function(t){t=t.replace(I,"\\$&").replace(S,"(?:$1)?").replace(H,function(t,e){return e?t:"([^/?]+)"}).replace(A,"([^?]*?)");return new RegExp("^"+t+"(?:\\?([\\s\\S]*))?$")},_extractParameters:function(t,e){var r=t.exec(e).slice(1);return i.map(r,function(t,e){if(e===r.length-1)return t||null;return t?decodeURIComponent(t):null})}});var N=e.History=function(){this.handlers=[];i.bindAll(this,"checkUrl");if(typeof window!=="undefined"){this.location=window.location;this.history=window.history}};var R=/^[#\/]|\s+$/g;var O=/^\/+|\/+$/g;var P=/msie [\w.]+/;var C=/\/$/;var j=/#.*$/;N.started=false;i.extend(N.prototype,u,{interval:50,atRoot:function(){return this.location.pathname.replace(/[^\/]$/,"$&/")===this.root},getHash:function(t){var e=(t||this).location.href.match(/#(.*)$/);return e?e[1]:""},getFragment:function(t,e){if(t==null){if(this._hasPushState||!this._wantsHashChange||e){t=decodeURI(this.location.pathname+this.location.search);var i=this.root.replace(C,"");if(!t.indexOf(i))t=t.slice(i.length)}else{t=this.getHash()}}return t.replace(R,"")},start:function(t){if(N.started)throw new Error("Backbone.history has already been started");N.started=true;this.options=i.extend({root:"/"},this.options,t);this.root=this.options.root;this._wantsHashChange=this.options.hashChange!==false;this._wantsPushState=!!this.options.pushState;this._hasPushState=!!(this.options.pushState&&this.history&&this.history.pushState);var r=this.getFragment();var s=document.documentMode;var n=P.exec(navigator.userAgent.toLowerCase())&&(!s||s<=7);this.root=("/"+this.root+"/").replace(O,"/");if(n&&this._wantsHashChange){var a=e.$('<iframe src="javascript:0" tabindex="-1">');this.iframe=a.hide().appendTo("body")[0].contentWindow;this.navigate(r)}if(this._hasPushState){e.$(window).on("popstate",this.checkUrl)}else if(this._wantsHashChange&&"onhashchange"in window&&!n){e.$(window).on("hashchange",this.checkUrl)}else if(this._wantsHashChange){this._checkUrlInterval=setInterval(this.checkUrl,this.interval)}this.fragment=r;var 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true}})},navigate:function(t,e){if(!N.started)return false;if(!e||e===true)e={trigger:!!e};var i=this.root+(t=this.getFragment(t||""));t=t.replace(j,"");if(this.fragment===t)return;this.fragment=t;if(t===""&&i!=="/")i=i.slice(0,-1);if(this._hasPushState){this.history[e.replace?"replaceState":"pushState"]({},document.title,i)}else if(this._wantsHashChange){this._updateHash(this.location,t,e.replace);if(this.iframe&&t!==this.getFragment(this.getHash(this.iframe))){if(!e.replace)this.iframe.document.open().close();this._updateHash(this.iframe.location,t,e.replace)}}else{return this.location.assign(i)}if(e.trigger)return this.loadUrl(t)},_updateHash:function(t,e,i){if(i){var r=t.href.replace(/(javascript:|#).*$/,"");t.replace(r+"#"+e)}else{t.hash="#"+e}}});e.history=new N;var U=function(t,e){var r=this;var s;if(t&&i.has(t,"constructor")){s=t.constructor}else{s=function(){return r.apply(this,arguments)}}i.extend(s,r,e);var 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e=this.get(this.idAttribute);return t.replace(/[^\/]$/,"$&/")+encodeURIComponent(e)},parse:function(t,e){return t},clone:function(){return new this.constructor(this.attributes)},isNew:function(){return!this.has(this.idAttribute)},isValid:function(t){return this._validate({},i.defaults({validate:true},t))},_validate:function(t,e){if(!e.validate||!this.validate)return true;t=i.extend({},this.attributes,t);var r=this.validationError=this.validate(t,e)||null;if(!r)return true;this.trigger("invalid",this,r,i.extend(e,{validationError:r}));return false}});var b={keys:1,values:1,pairs:1,invert:1,pick:0,omit:0,chain:1,isEmpty:1};o(y,b,"attributes");var x=e.Collection=function(t,e){e||(e={});if(e.model)this.model=e.model;if(e.comparator!==void 0)this.comparator=e.comparator;this._reset();this.initialize.apply(this,arguments);if(t)this.reset(t,i.extend({silent:true},e))};var w={add:true,remove:true,merge:true};var E={add:true,remove:false};var k=function(t,e,i){i=Math.min(Math.max(i,0),t.length);var r=Array(t.length-i);var n=e.length;for(var s=0;s<r.length;s++)r[s]=t[s+i];for(s=0;s<n;s++)t[s+i]=e[s];for(s=0;s<r.length;s++)t[s+n+i]=r[s]};i.extend(x.prototype,l,{model:y,initialize:function(){},toJSON:function(t){return this.map(function(e){return e.toJSON(t)})},sync:function(){return e.sync.apply(this,arguments)},add:function(t,e){return this.set(t,i.extend({merge:false},e,E))},remove:function(t,e){e=i.extend({},e);var r=!i.isArray(t);t=r?[t]:i.clone(t);var n=this._removeModels(t,e);if(!e.silent&&n)this.trigger("update",this,e);return r?n[0]:n},set:function(t,e){if(t==null)return;e=i.defaults({},e,w);if(e.parse&&!this._isModel(t))t=this.parse(t,e);var r=!i.isArray(t);t=r?[t]:t.slice();var n=e.at;if(n!=null)n=+n;if(n<0)n+=this.length+1;var s=[];var a=[];var o=[];var h={};var u=e.add;var l=e.merge;var c=e.remove;var f=false;var d=this.comparator&&n==null&&e.sort!==false;var v=i.isString(this.comparator)?this.comparator:null;var g;for(var p=0;p<t.length;p++){g=t[p];var m=this.get(g);if(m){if(l&&g!==m){var _=this._isModel(g)?g.attributes:g;if(e.parse)_=m.parse(_,e);m.set(_,e);if(d&&!f)f=m.hasChanged(v)}if(!h[m.cid]){h[m.cid]=true;s.push(m)}t[p]=m}else if(u){g=t[p]=this._prepareModel(g,e);if(g){a.push(g);this._addReference(g,e);h[g.cid]=true;s.push(g)}}}if(c){for(p=0;p<this.length;p++){g=this.models[p];if(!h[g.cid])o.push(g)}if(o.length)this._removeModels(o,e)}var y=false;var b=!d&&u&&c;if(s.length&&b){y=this.length!=s.length||i.some(this.models,function(t,e){return t!==s[e]});this.models.length=0;k(this.models,s,0);this.length=this.models.length}else if(a.length){if(d)f=true;k(this.models,a,n==null?this.length:n);this.length=this.models.length}if(f)this.sort({silent:true});if(!e.silent){for(p=0;p<a.length;p++){if(n!=null)e.index=n+p;g=a[p];g.trigger("add",g,this,e)}if(f||y)this.trigger("sort",this,e);if(a.length||o.length)this.trigger("update",this,e)}return r?t[0]:t},reset:function(t,e){e=e?i.clone(e):{};for(var r=0;r<this.models.length;r++){this._removeReference(this.models[r],e)}e.previousModels=this.models;this._reset();t=this.add(t,i.extend({silent:true},e));if(!e.silent)this.trigger("reset",this,e);return t},push:function(t,e){return this.add(t,i.extend({at:this.length},e))},pop:function(t){var e=this.at(this.length-1);return this.remove(e,t)},unshift:function(t,e){return this.add(t,i.extend({at:0},e))},shift:function(t){var e=this.at(0);return this.remove(e,t)},slice:function(){return s.apply(this.models,arguments)},get:function(t){if(t==null)return void 0;var e=this.modelId(this._isModel(t)?t.attributes:t);return this._byId[t]||this._byId[e]||this._byId[t.cid]},at:function(t){if(t<0)t+=this.length;return this.models[t]},where:function(t,e){return this[e?"find":"filter"](t)},findWhere:function(t){return this.where(t,true)},sort:function(t){var e=this.comparator;if(!e)throw new Error("Cannot sort a set without a comparator");t||(t={});var r=e.length;if(i.isFunction(e))e=i.bind(e,this);if(r===1||i.isString(e)){this.models=this.sortBy(e)}else{this.models.sort(e)}if(!t.silent)this.trigger("sort",this,t);return this},pluck:function(t){return i.invoke(this.models,"get",t)},fetch:function(t){t=i.extend({parse:true},t);var e=t.success;var r=this;t.success=function(i){var n=t.reset?"reset":"set";r[n](i,t);if(e)e.call(t.context,r,i,t);r.trigger("sync",r,i,t)};z(this,t);return this.sync("read",this,t)},create:function(t,e){e=e?i.clone(e):{};var r=e.wait;t=this._prepareModel(t,e);if(!t)return false;if(!r)this.add(t,e);var n=this;var s=e.success;e.success=function(t,e,i){if(r)n.add(t,i);if(s)s.call(i.context,t,e,i)};t.save(null,e);return t},parse:function(t,e){return t},clone:function(){return new this.constructor(this.models,{model:this.model,comparator:this.comparator})},modelId:function(t){return t[this.model.prototype.idAttribute||"id"]},_reset:function(){this.length=0;this.models=[];this._byId={}},_prepareModel:function(t,e){if(this._isModel(t)){if(!t.collection)t.collection=this;return t}e=e?i.clone(e):{};e.collection=this;var r=new this.model(t,e);if(!r.validationError)return r;this.trigger("invalid",this,r.validationError,e);return false},_removeModels:function(t,e){var i=[];for(var r=0;r<t.length;r++){var n=this.get(t[r]);if(!n)continue;var s=this.indexOf(n);this.models.splice(s,1);this.length--;if(!e.silent){e.index=s;n.trigger("remove",n,this,e)}i.push(n);this._removeReference(n,e)}return i.length?i:false},_isModel:function(t){return t instanceof y},_addReference:function(t,e){this._byId[t.cid]=t;var i=this.modelId(t.attributes);if(i!=null)this._byId[i]=t;t.on("all",this._onModelEvent,this)},_removeReference:function(t,e){delete this._byId[t.cid];var i=this.modelId(t.attributes);if(i!=null)delete this._byId[i];if(this===t.collection)delete t.collection;t.off("all",this._onModelEvent,this)},_onModelEvent:function(t,e,i,r){if((t==="add"||t==="remove")&&i!==this)return;if(t==="destroy")this.remove(e,r);if(t==="change"){var n=this.modelId(e.previousAttributes());var s=this.modelId(e.attributes);if(n!==s){if(n!=null)delete this._byId[n];if(s!=null)this._byId[s]=e}}this.trigger.apply(this,arguments)}});var S={forEach:3,each:3,map:3,collect:3,reduce:4,foldl:4,inject:4,reduceRight:4,foldr:4,find:3,detect:3,filter:3,select:3,reject:3,every:3,all:3,some:3,any:3,include: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};o(x,S,"models");var I=e.View=function(t){this.cid=i.uniqueId("view");i.extend(this,i.pick(t,P));this._ensureElement();this.initialize.apply(this,arguments)};var T=/^(\S+)\s*(.*)$/;var P=["model","collection","el","id","attributes","className","tagName","events"];i.extend(I.prototype,l,{tagName:"div",$:function(t){return this.$el.find(t)},initialize:function(){},render:function(){return this},remove:function(){this._removeElement();this.stopListening();return this},_removeElement:function(){this.$el.remove()},setElement:function(t){this.undelegateEvents();this._setElement(t);this.delegateEvents();return this},_setElement:function(t){this.$el=t instanceof e.$?t:e.$(t);this.el=this.$el[0]},delegateEvents:function(t){t||(t=i.result(this,"events"));if(!t)return this;this.undelegateEvents();for(var e in t){var r=t[e];if(!i.isFunction(r))r=this[r];if(!r)continue;var n=e.match(T);this.delegate(n[1],n[2],i.bind(r,this))}return this},delegate:function(t,e,i){this.$el.on(t+".delegateEvents"+this.cid,e,i);return this},undelegateEvents:function(){if(this.$el)this.$el.off(".delegateEvents"+this.cid);return 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Index: src/wp-includes/js/underscore.js
===================================================================
--- src/wp-includes/js/underscore.js	(revision 36320)
+++ src/wp-includes/js/underscore.js	(working copy)
@@ -1,6 +1,6 @@
-//     Underscore.js 1.6.0
+//     Underscore.js 1.8.3
 //     http://underscorejs.org
-//     (c) 2009-2014 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
+//     (c) 2009-2015 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 //     Underscore may be freely distributed under the MIT license.
 
 (function() {
@@ -14,9 +14,6 @@
   // Save the previous value of the `_` variable.
   var previousUnderscore = root._;
 
-  // Establish the object that gets returned to break out of a loop iteration.
-  var breaker = {};
-
   // Save bytes in the minified (but not gzipped) version:
   var ArrayProto = Array.prototype, ObjProto = Object.prototype, FuncProto = Function.prototype;
 
@@ -24,7 +21,6 @@
   var
     push             = ArrayProto.push,
     slice            = ArrayProto.slice,
-    concat           = ArrayProto.concat,
     toString         = ObjProto.toString,
     hasOwnProperty   = ObjProto.hasOwnProperty;
 
@@ -31,19 +27,14 @@
   // All **ECMAScript 5** native function implementations that we hope to use
   // are declared here.
   var
-    nativeForEach      = ArrayProto.forEach,
-    nativeMap          = ArrayProto.map,
-    nativeReduce       = ArrayProto.reduce,
-    nativeReduceRight  = ArrayProto.reduceRight,
-    nativeFilter       = ArrayProto.filter,
-    nativeEvery        = ArrayProto.every,
-    nativeSome         = ArrayProto.some,
-    nativeIndexOf      = ArrayProto.indexOf,
-    nativeLastIndexOf  = ArrayProto.lastIndexOf,
     nativeIsArray      = Array.isArray,
     nativeKeys         = Object.keys,
-    nativeBind         = FuncProto.bind;
+    nativeBind         = FuncProto.bind,
+    nativeCreate       = Object.create;
 
+  // Naked function reference for surrogate-prototype-swapping.
+  var Ctor = function(){};
+
   // Create a safe reference to the Underscore object for use below.
   var _ = function(obj) {
     if (obj instanceof _) return obj;
@@ -53,8 +44,7 @@
 
   // Export the Underscore object for **Node.js**, with
   // backwards-compatibility for the old `require()` API. If we're in
-  // the browser, add `_` as a global object via a string identifier,
-  // for Closure Compiler "advanced" mode.
+  // the browser, add `_` as a global object.
   if (typeof exports !== 'undefined') {
     if (typeof module !== 'undefined' && module.exports) {
       exports = module.exports = _;
@@ -65,114 +55,176 @@
   }
 
   // Current version.
-  _.VERSION = '1.6.0';
+  _.VERSION = '1.8.3';
 
+  // Internal function that returns an efficient (for current engines) version
+  // of the passed-in callback, to be repeatedly applied in other Underscore
+  // functions.
+  var optimizeCb = function(func, context, argCount) {
+    if (context === void 0) return func;
+    switch (argCount == null ? 3 : argCount) {
+      case 1: return function(value) {
+        return func.call(context, value);
+      };
+      case 2: return function(value, other) {
+        return func.call(context, value, other);
+      };
+      case 3: return function(value, index, collection) {
+        return func.call(context, value, index, collection);
+      };
+      case 4: return function(accumulator, value, index, collection) {
+        return func.call(context, accumulator, value, index, collection);
+      };
+    }
+    return function() {
+      return func.apply(context, arguments);
+    };
+  };
+
+  // A mostly-internal function to generate callbacks that can be applied
+  // to each element in a collection, returning the desired result — either
+  // identity, an arbitrary callback, a property matcher, or a property accessor.
+  var cb = function(value, context, argCount) {
+    if (value == null) return _.identity;
+    if (_.isFunction(value)) return optimizeCb(value, context, argCount);
+    if (_.isObject(value)) return _.matcher(value);
+    return _.property(value);
+  };
+  _.iteratee = function(value, context) {
+    return cb(value, context, Infinity);
+  };
+
+  // An internal function for creating assigner functions.
+  var createAssigner = function(keysFunc, undefinedOnly) {
+    return function(obj) {
+      var length = arguments.length;
+      if (length < 2 || obj == null) return obj;
+      for (var index = 1; index < length; index++) {
+        var source = arguments[index],
+            keys = keysFunc(source),
+            l = keys.length;
+        for (var i = 0; i < l; i++) {
+          var key = keys[i];
+          if (!undefinedOnly || obj[key] === void 0) obj[key] = source[key];
+        }
+      }
+      return obj;
+    };
+  };
+
+  // An internal function for creating a new object that inherits from another.
+  var baseCreate = function(prototype) {
+    if (!_.isObject(prototype)) return {};
+    if (nativeCreate) return nativeCreate(prototype);
+    Ctor.prototype = prototype;
+    var result = new Ctor;
+    Ctor.prototype = null;
+    return result;
+  };
+
+  var property = function(key) {
+    return function(obj) {
+      return obj == null ? void 0 : obj[key];
+    };
+  };
+
+  // Helper for collection methods to determine whether a collection
+  // should be iterated as an array or as an object
+  // Related: http://people.mozilla.org/~jorendorff/es6-draft.html#sec-tolength
+  // Avoids a very nasty iOS 8 JIT bug on ARM-64. #2094
+  var MAX_ARRAY_INDEX = Math.pow(2, 53) - 1;
+  var getLength = property('length');
+  var isArrayLike = function(collection) {
+    var length = getLength(collection);
+    return typeof length == 'number' && length >= 0 && length <= MAX_ARRAY_INDEX;
+  };
+
   // Collection Functions
   // --------------------
 
   // The cornerstone, an `each` implementation, aka `forEach`.
-  // Handles objects with the built-in `forEach`, arrays, and raw objects.
-  // Delegates to **ECMAScript 5**'s native `forEach` if available.
-  var each = _.each = _.forEach = function(obj, iterator, context) {
-    if (obj == null) return obj;
-    if (nativeForEach && obj.forEach === nativeForEach) {
-      obj.forEach(iterator, context);
-    } else if (obj.length === +obj.length) {
-      for (var i = 0, length = obj.length; i < length; i++) {
-        if (iterator.call(context, obj[i], i, obj) === breaker) return;
+  // Handles raw objects in addition to array-likes. Treats all
+  // sparse array-likes as if they were dense.
+  _.each = _.forEach = function(obj, iteratee, context) {
+    iteratee = optimizeCb(iteratee, context);
+    var i, length;
+    if (isArrayLike(obj)) {
+      for (i = 0, length = obj.length; i < length; i++) {
+        iteratee(obj[i], i, obj);
       }
     } else {
       var keys = _.keys(obj);
-      for (var i = 0, length = keys.length; i < length; i++) {
-        if (iterator.call(context, obj[keys[i]], keys[i], obj) === breaker) return;
+      for (i = 0, length = keys.length; i < length; i++) {
+        iteratee(obj[keys[i]], keys[i], obj);
       }
     }
     return obj;
   };
 
-  // Return the results of applying the iterator to each element.
-  // Delegates to **ECMAScript 5**'s native `map` if available.
-  _.map = _.collect = function(obj, iterator, context) {
-    var results = [];
-    if (obj == null) return results;
-    if (nativeMap && obj.map === nativeMap) return obj.map(iterator, context);
-    each(obj, function(value, index, list) {
-      results.push(iterator.call(context, value, index, list));
-    });
+  // Return the results of applying the iteratee to each element.
+  _.map = _.collect = function(obj, iteratee, context) {
+    iteratee = cb(iteratee, context);
+    var keys = !isArrayLike(obj) && _.keys(obj),
+        length = (keys || obj).length,
+        results = Array(length);
+    for (var index = 0; index < length; index++) {
+      var currentKey = keys ? keys[index] : index;
+      results[index] = iteratee(obj[currentKey], currentKey, obj);
+    }
     return results;
   };
 
-  var reduceError = 'Reduce of empty array with no initial value';
+  // Create a reducing function iterating left or right.
+  function createReduce(dir) {
+    // Optimized iterator function as using arguments.length
+    // in the main function will deoptimize the, see #1991.
+    function iterator(obj, iteratee, memo, keys, index, length) {
+      for (; index >= 0 && index < length; index += dir) {
+        var currentKey = keys ? keys[index] : index;
+        memo = iteratee(memo, obj[currentKey], currentKey, obj);
+      }
+      return memo;
+    }
 
-  // **Reduce** builds up a single result from a list of values, aka `inject`,
-  // or `foldl`. Delegates to **ECMAScript 5**'s native `reduce` if available.
-  _.reduce = _.foldl = _.inject = function(obj, iterator, memo, context) {
-    var initial = arguments.length > 2;
-    if (obj == null) obj = [];
-    if (nativeReduce && obj.reduce === nativeReduce) {
-      if (context) iterator = _.bind(iterator, context);
-      return initial ? obj.reduce(iterator, memo) : obj.reduce(iterator);
-    }
-    each(obj, function(value, index, list) {
-      if (!initial) {
-        memo = value;
-        initial = true;
-      } else {
-        memo = iterator.call(context, memo, value, index, list);
+    return function(obj, iteratee, memo, context) {
+      iteratee = optimizeCb(iteratee, context, 4);
+      var keys = !isArrayLike(obj) && _.keys(obj),
+          length = (keys || obj).length,
+          index = dir > 0 ? 0 : length - 1;
+      // Determine the initial value if none is provided.
+      if (arguments.length < 3) {
+        memo = obj[keys ? keys[index] : index];
+        index += dir;
       }
-    });
-    if (!initial) throw new TypeError(reduceError);
-    return memo;
-  };
+      return iterator(obj, iteratee, memo, keys, index, length);
+    };
+  }
 
+  // **Reduce** builds up a single result from a list of values, aka `inject`,
+  // or `foldl`.
+  _.reduce = _.foldl = _.inject = createReduce(1);
+
   // The right-associative version of reduce, also known as `foldr`.
-  // Delegates to **ECMAScript 5**'s native `reduceRight` if available.
-  _.reduceRight = _.foldr = function(obj, iterator, memo, context) {
-    var initial = arguments.length > 2;
-    if (obj == null) obj = [];
-    if (nativeReduceRight && obj.reduceRight === nativeReduceRight) {
-      if (context) iterator = _.bind(iterator, context);
-      return initial ? obj.reduceRight(iterator, memo) : obj.reduceRight(iterator);
-    }
-    var length = obj.length;
-    if (length !== +length) {
-      var keys = _.keys(obj);
-      length = keys.length;
-    }
-    each(obj, function(value, index, list) {
-      index = keys ? keys[--length] : --length;
-      if (!initial) {
-        memo = obj[index];
-        initial = true;
-      } else {
-        memo = iterator.call(context, memo, obj[index], index, list);
-      }
-    });
-    if (!initial) throw new TypeError(reduceError);
-    return memo;
-  };
+  _.reduceRight = _.foldr = createReduce(-1);
 
   // Return the first value which passes a truth test. Aliased as `detect`.
   _.find = _.detect = function(obj, predicate, context) {
-    var result;
-    any(obj, function(value, index, list) {
-      if (predicate.call(context, value, index, list)) {
-        result = value;
-        return true;
-      }
-    });
-    return result;
+    var key;
+    if (isArrayLike(obj)) {
+      key = _.findIndex(obj, predicate, context);
+    } else {
+      key = _.findKey(obj, predicate, context);
+    }
+    if (key !== void 0 && key !== -1) return obj[key];
   };
 
   // Return all the elements that pass a truth test.
-  // Delegates to **ECMAScript 5**'s native `filter` if available.
   // Aliased as `select`.
   _.filter = _.select = function(obj, predicate, context) {
     var results = [];
-    if (obj == null) return results;
-    if (nativeFilter && obj.filter === nativeFilter) return obj.filter(predicate, context);
-    each(obj, function(value, index, list) {
-      if (predicate.call(context, value, index, list)) results.push(value);
+    predicate = cb(predicate, context);
+    _.each(obj, function(value, index, list) {
+      if (predicate(value, index, list)) results.push(value);
     });
     return results;
   };
@@ -179,47 +231,41 @@
 
   // Return all the elements for which a truth test fails.
   _.reject = function(obj, predicate, context) {
-    return _.filter(obj, function(value, index, list) {
-      return !predicate.call(context, value, index, list);
-    }, context);
+    return _.filter(obj, _.negate(cb(predicate)), context);
   };
 
   // Determine whether all of the elements match a truth test.
-  // Delegates to **ECMAScript 5**'s native `every` if available.
   // Aliased as `all`.
   _.every = _.all = function(obj, predicate, context) {
-    predicate || (predicate = _.identity);
-    var result = true;
-    if (obj == null) return result;
-    if (nativeEvery && obj.every === nativeEvery) return obj.every(predicate, context);
-    each(obj, function(value, index, list) {
-      if (!(result = result && predicate.call(context, value, index, list))) return breaker;
-    });
-    return !!result;
+    predicate = cb(predicate, context);
+    var keys = !isArrayLike(obj) && _.keys(obj),
+        length = (keys || obj).length;
+    for (var index = 0; index < length; index++) {
+      var currentKey = keys ? keys[index] : index;
+      if (!predicate(obj[currentKey], currentKey, obj)) return false;
+    }
+    return true;
   };
 
   // Determine if at least one element in the object matches a truth test.
-  // Delegates to **ECMAScript 5**'s native `some` if available.
   // Aliased as `any`.
-  var any = _.some = _.any = function(obj, predicate, context) {
-    predicate || (predicate = _.identity);
-    var result = false;
-    if (obj == null) return result;
-    if (nativeSome && obj.some === nativeSome) return obj.some(predicate, context);
-    each(obj, function(value, index, list) {
-      if (result || (result = predicate.call(context, value, index, list))) return breaker;
-    });
-    return !!result;
+  _.some = _.any = function(obj, predicate, context) {
+    predicate = cb(predicate, context);
+    var keys = !isArrayLike(obj) && _.keys(obj),
+        length = (keys || obj).length;
+    for (var index = 0; index < length; index++) {
+      var currentKey = keys ? keys[index] : index;
+      if (predicate(obj[currentKey], currentKey, obj)) return true;
+    }
+    return false;
   };
 
-  // Determine if the array or object contains a given value (using `===`).
-  // Aliased as `include`.
-  _.contains = _.include = function(obj, target) {
-    if (obj == null) return false;
-    if (nativeIndexOf && obj.indexOf === nativeIndexOf) return obj.indexOf(target) != -1;
-    return any(obj, function(value) {
-      return value === target;
-    });
+  // Determine if the array or object contains a given item (using `===`).
+  // Aliased as `includes` and `include`.
+  _.contains = _.includes = _.include = function(obj, item, fromIndex, guard) {
+    if (!isArrayLike(obj)) obj = _.values(obj);
+    if (typeof fromIndex != 'number' || guard) fromIndex = 0;
+    return _.indexOf(obj, item, fromIndex) >= 0;
   };
 
   // Invoke a method (with arguments) on every item in a collection.
@@ -227,7 +273,8 @@
     var args = slice.call(arguments, 2);
     var isFunc = _.isFunction(method);
     return _.map(obj, function(value) {
-      return (isFunc ? method : value[method]).apply(value, args);
+      var func = isFunc ? method : value[method];
+      return func == null ? func : func.apply(value, args);
     });
   };
 
@@ -239,60 +286,76 @@
   // Convenience version of a common use case of `filter`: selecting only objects
   // containing specific `key:value` pairs.
   _.where = function(obj, attrs) {
-    return _.filter(obj, _.matches(attrs));
+    return _.filter(obj, _.matcher(attrs));
   };
 
   // Convenience version of a common use case of `find`: getting the first object
   // containing specific `key:value` pairs.
   _.findWhere = function(obj, attrs) {
-    return _.find(obj, _.matches(attrs));
+    return _.find(obj, _.matcher(attrs));
   };
 
-  // Return the maximum element or (element-based computation).
-  // Can't optimize arrays of integers longer than 65,535 elements.
-  // See [WebKit Bug 80797](https://bugs.webkit.org/show_bug.cgi?id=80797)
-  _.max = function(obj, iterator, context) {
-    if (!iterator && _.isArray(obj) && obj[0] === +obj[0] && obj.length < 65535) {
-      return Math.max.apply(Math, obj);
+  // Return the maximum element (or element-based computation).
+  _.max = function(obj, iteratee, context) {
+    var result = -Infinity, lastComputed = -Infinity,
+        value, computed;
+    if (iteratee == null && obj != null) {
+      obj = isArrayLike(obj) ? obj : _.values(obj);
+      for (var i = 0, length = obj.length; i < length; i++) {
+        value = obj[i];
+        if (value > result) {
+          result = value;
+        }
+      }
+    } else {
+      iteratee = cb(iteratee, context);
+      _.each(obj, function(value, index, list) {
+        computed = iteratee(value, index, list);
+        if (computed > lastComputed || computed === -Infinity && result === -Infinity) {
+          result = value;
+          lastComputed = computed;
+        }
+      });
     }
-    var result = -Infinity, lastComputed = -Infinity;
-    each(obj, function(value, index, list) {
-      var computed = iterator ? iterator.call(context, value, index, list) : value;
-      if (computed > lastComputed) {
-        result = value;
-        lastComputed = computed;
-      }
-    });
     return result;
   };
 
   // Return the minimum element (or element-based computation).
-  _.min = function(obj, iterator, context) {
-    if (!iterator && _.isArray(obj) && obj[0] === +obj[0] && obj.length < 65535) {
-      return Math.min.apply(Math, obj);
+  _.min = function(obj, iteratee, context) {
+    var result = Infinity, lastComputed = Infinity,
+        value, computed;
+    if (iteratee == null && obj != null) {
+      obj = isArrayLike(obj) ? obj : _.values(obj);
+      for (var i = 0, length = obj.length; i < length; i++) {
+        value = obj[i];
+        if (value < result) {
+          result = value;
+        }
+      }
+    } else {
+      iteratee = cb(iteratee, context);
+      _.each(obj, function(value, index, list) {
+        computed = iteratee(value, index, list);
+        if (computed < lastComputed || computed === Infinity && result === Infinity) {
+          result = value;
+          lastComputed = computed;
+        }
+      });
     }
-    var result = Infinity, lastComputed = Infinity;
-    each(obj, function(value, index, list) {
-      var computed = iterator ? iterator.call(context, value, index, list) : value;
-      if (computed < lastComputed) {
-        result = value;
-        lastComputed = computed;
-      }
-    });
     return result;
   };
 
-  // Shuffle an array, using the modern version of the
+  // Shuffle a collection, using the modern version of the
   // [Fisher-Yates shuffle](http://en.wikipedia.org/wiki/Fisher–Yates_shuffle).
   _.shuffle = function(obj) {
-    var rand;
-    var index = 0;
-    var shuffled = [];
-    each(obj, function(value) {
-      rand = _.random(index++);
-      shuffled[index - 1] = shuffled[rand];
-      shuffled[rand] = value;
-    });
+    var set = isArrayLike(obj) ? obj : _.values(obj);
+    var length = set.length;
+    var shuffled = Array(length);
+    for (var index = 0, rand; index < length; index++) {
+      rand = _.random(0, index);
+      if (rand !== index) shuffled[index] = shuffled[rand];
+      shuffled[rand] = set[index];
+    }
     return shuffled;
   };
 
@@ -301,27 +364,20 @@
   // The internal `guard` argument allows it to work with `map`.
   _.sample = function(obj, n, guard) {
     if (n == null || guard) {
-      if (obj.length !== +obj.length) obj = _.values(obj);
+      if (!isArrayLike(obj)) obj = _.values(obj);
       return obj[_.random(obj.length - 1)];
     }
     return _.shuffle(obj).slice(0, Math.max(0, n));
   };
 
-  // An internal function to generate lookup iterators.
-  var lookupIterator = function(value) {
-    if (value == null) return _.identity;
-    if (_.isFunction(value)) return value;
-    return _.property(value);
-  };
-
-  // Sort the object's values by a criterion produced by an iterator.
-  _.sortBy = function(obj, iterator, context) {
-    iterator = lookupIterator(iterator);
+  // Sort the object's values by a criterion produced by an iteratee.
+  _.sortBy = function(obj, iteratee, context) {
+    iteratee = cb(iteratee, context);
     return _.pluck(_.map(obj, function(value, index, list) {
       return {
         value: value,
         index: index,
-        criteria: iterator.call(context, value, index, list)
+        criteria: iteratee(value, index, list)
       };
     }).sort(function(left, right) {
       var a = left.criteria;
@@ -336,12 +392,12 @@
 
   // An internal function used for aggregate "group by" operations.
   var group = function(behavior) {
-    return function(obj, iterator, context) {
+    return function(obj, iteratee, context) {
       var result = {};
-      iterator = lookupIterator(iterator);
-      each(obj, function(value, index) {
-        var key = iterator.call(context, value, index, obj);
-        behavior(result, key, value);
+      iteratee = cb(iteratee, context);
+      _.each(obj, function(value, index) {
+        var key = iteratee(value, index, obj);
+        behavior(result, value, key);
       });
       return result;
     };
@@ -349,13 +405,13 @@
 
   // Groups the object's values by a criterion. Pass either a string attribute
   // to group by, or a function that returns the criterion.
-  _.groupBy = group(function(result, key, value) {
-    _.has(result, key) ? result[key].push(value) : result[key] = [value];
+  _.groupBy = group(function(result, value, key) {
+    if (_.has(result, key)) result[key].push(value); else result[key] = [value];
   });
 
   // Indexes the object's values by a criterion, similar to `groupBy`, but for
   // when you know that your index values will be unique.
-  _.indexBy = group(function(result, key, value) {
+  _.indexBy = group(function(result, value, key) {
     result[key] = value;
   });
 
@@ -362,28 +418,15 @@
   // Counts instances of an object that group by a certain criterion. Pass
   // either a string attribute to count by, or a function that returns the
   // criterion.
-  _.countBy = group(function(result, key) {
-    _.has(result, key) ? result[key]++ : result[key] = 1;
+  _.countBy = group(function(result, value, key) {
+    if (_.has(result, key)) result[key]++; else result[key] = 1;
   });
 
-  // Use a comparator function to figure out the smallest index at which
-  // an object should be inserted so as to maintain order. Uses binary search.
-  _.sortedIndex = function(array, obj, iterator, context) {
-    iterator = lookupIterator(iterator);
-    var value = iterator.call(context, obj);
-    var low = 0, high = array.length;
-    while (low < high) {
-      var mid = (low + high) >>> 1;
-      iterator.call(context, array[mid]) < value ? low = mid + 1 : high = mid;
-    }
-    return low;
-  };
-
   // Safely create a real, live array from anything iterable.
   _.toArray = function(obj) {
     if (!obj) return [];
     if (_.isArray(obj)) return slice.call(obj);
-    if (obj.length === +obj.length) return _.map(obj, _.identity);
+    if (isArrayLike(obj)) return _.map(obj, _.identity);
     return _.values(obj);
   };
 
@@ -390,9 +433,20 @@
   // Return the number of elements in an object.
   _.size = function(obj) {
     if (obj == null) return 0;
-    return (obj.length === +obj.length) ? obj.length : _.keys(obj).length;
+    return isArrayLike(obj) ? obj.length : _.keys(obj).length;
   };
 
+  // Split a collection into two arrays: one whose elements all satisfy the given
+  // predicate, and one whose elements all do not satisfy the predicate.
+  _.partition = function(obj, predicate, context) {
+    predicate = cb(predicate, context);
+    var pass = [], fail = [];
+    _.each(obj, function(value, key, obj) {
+      (predicate(value, key, obj) ? pass : fail).push(value);
+    });
+    return [pass, fail];
+  };
+
   // Array Functions
   // ---------------
 
@@ -401,33 +455,30 @@
   // allows it to work with `_.map`.
   _.first = _.head = _.take = function(array, n, guard) {
     if (array == null) return void 0;
-    if ((n == null) || guard) return array[0];
-    if (n < 0) return [];
-    return slice.call(array, 0, n);
+    if (n == null || guard) return array[0];
+    return _.initial(array, array.length - n);
   };
 
   // Returns everything but the last entry of the array. Especially useful on
   // the arguments object. Passing **n** will return all the values in
-  // the array, excluding the last N. The **guard** check allows it to work with
-  // `_.map`.
+  // the array, excluding the last N.
   _.initial = function(array, n, guard) {
-    return slice.call(array, 0, array.length - ((n == null) || guard ? 1 : n));
+    return slice.call(array, 0, Math.max(0, array.length - (n == null || guard ? 1 : n)));
   };
 
   // Get the last element of an array. Passing **n** will return the last N
-  // values in the array. The **guard** check allows it to work with `_.map`.
+  // values in the array.
   _.last = function(array, n, guard) {
     if (array == null) return void 0;
-    if ((n == null) || guard) return array[array.length - 1];
-    return slice.call(array, Math.max(array.length - n, 0));
+    if (n == null || guard) return array[array.length - 1];
+    return _.rest(array, Math.max(0, array.length - n));
   };
 
   // Returns everything but the first entry of the array. Aliased as `tail` and `drop`.
   // Especially useful on the arguments object. Passing an **n** will return
-  // the rest N values in the array. The **guard**
-  // check allows it to work with `_.map`.
+  // the rest N values in the array.
   _.rest = _.tail = _.drop = function(array, n, guard) {
-    return slice.call(array, (n == null) || guard ? 1 : n);
+    return slice.call(array, n == null || guard ? 1 : n);
   };
 
   // Trim out all falsy values from an array.
@@ -436,23 +487,28 @@
   };
 
   // Internal implementation of a recursive `flatten` function.
-  var flatten = function(input, shallow, output) {
-    if (shallow && _.every(input, _.isArray)) {
-      return concat.apply(output, input);
+  var flatten = function(input, shallow, strict, startIndex) {
+    var output = [], idx = 0;
+    for (var i = startIndex || 0, length = getLength(input); i < length; i++) {
+      var value = input[i];
+      if (isArrayLike(value) && (_.isArray(value) || _.isArguments(value))) {
+        //flatten current level of array or arguments object
+        if (!shallow) value = flatten(value, shallow, strict);
+        var j = 0, len = value.length;
+        output.length += len;
+        while (j < len) {
+          output[idx++] = value[j++];
+        }
+      } else if (!strict) {
+        output[idx++] = value;
+      }
     }
-    each(input, function(value) {
-      if (_.isArray(value) || _.isArguments(value)) {
-        shallow ? push.apply(output, value) : flatten(value, shallow, output);
-      } else {
-        output.push(value);
-      }
-    });
     return output;
   };
 
   // Flatten out an array, either recursively (by default), or just one level.
   _.flatten = function(array, shallow) {
-    return flatten(array, shallow, []);
+    return flatten(array, shallow, false);
   };
 
   // Return a version of the array that does not contain the specified value(s).
@@ -460,70 +516,83 @@
     return _.difference(array, slice.call(arguments, 1));
   };
 
-  // Split an array into two arrays: one whose elements all satisfy the given
-  // predicate, and one whose elements all do not satisfy the predicate.
-  _.partition = function(array, predicate) {
-    var pass = [], fail = [];
-    each(array, function(elem) {
-      (predicate(elem) ? pass : fail).push(elem);
-    });
-    return [pass, fail];
-  };
-
   // Produce a duplicate-free version of the array. If the array has already
   // been sorted, you have the option of using a faster algorithm.
   // Aliased as `unique`.
-  _.uniq = _.unique = function(array, isSorted, iterator, context) {
-    if (_.isFunction(isSorted)) {
-      context = iterator;
-      iterator = isSorted;
+  _.uniq = _.unique = function(array, isSorted, iteratee, context) {
+    if (!_.isBoolean(isSorted)) {
+      context = iteratee;
+      iteratee = isSorted;
       isSorted = false;
     }
-    var initial = iterator ? _.map(array, iterator, context) : array;
-    var results = [];
+    if (iteratee != null) iteratee = cb(iteratee, context);
+    var result = [];
     var seen = [];
-    each(initial, function(value, index) {
-      if (isSorted ? (!index || seen[seen.length - 1] !== value) : !_.contains(seen, value)) {
-        seen.push(value);
-        results.push(array[index]);
+    for (var i = 0, length = getLength(array); i < length; i++) {
+      var value = array[i],
+          computed = iteratee ? iteratee(value, i, array) : value;
+      if (isSorted) {
+        if (!i || seen !== computed) result.push(value);
+        seen = computed;
+      } else if (iteratee) {
+        if (!_.contains(seen, computed)) {
+          seen.push(computed);
+          result.push(value);
+        }
+      } else if (!_.contains(result, value)) {
+        result.push(value);
       }
-    });
-    return results;
+    }
+    return result;
   };
 
   // Produce an array that contains the union: each distinct element from all of
   // the passed-in arrays.
   _.union = function() {
-    return _.uniq(_.flatten(arguments, true));
+    return _.uniq(flatten(arguments, true, true));
   };
 
   // Produce an array that contains every item shared between all the
   // passed-in arrays.
   _.intersection = function(array) {
-    var rest = slice.call(arguments, 1);
-    return _.filter(_.uniq(array), function(item) {
-      return _.every(rest, function(other) {
-        return _.contains(other, item);
-      });
-    });
+    var result = [];
+    var argsLength = arguments.length;
+    for (var i = 0, length = getLength(array); i < length; i++) {
+      var item = array[i];
+      if (_.contains(result, item)) continue;
+      for (var j = 1; j < argsLength; j++) {
+        if (!_.contains(arguments[j], item)) break;
+      }
+      if (j === argsLength) result.push(item);
+    }
+    return result;
   };
 
   // Take the difference between one array and a number of other arrays.
   // Only the elements present in just the first array will remain.
   _.difference = function(array) {
-    var rest = concat.apply(ArrayProto, slice.call(arguments, 1));
-    return _.filter(array, function(value){ return !_.contains(rest, value); });
+    var rest = flatten(arguments, true, true, 1);
+    return _.filter(array, function(value){
+      return !_.contains(rest, value);
+    });
   };
 
   // Zip together multiple lists into a single array -- elements that share
   // an index go together.
   _.zip = function() {
-    var length = _.max(_.pluck(arguments, 'length').concat(0));
-    var results = new Array(length);
-    for (var i = 0; i < length; i++) {
-      results[i] = _.pluck(arguments, '' + i);
+    return _.unzip(arguments);
+  };
+
+  // Complement of _.zip. Unzip accepts an array of arrays and groups
+  // each array's elements on shared indices
+  _.unzip = function(array) {
+    var length = array && _.max(array, getLength).length || 0;
+    var result = Array(length);
+
+    for (var index = 0; index < length; index++) {
+      result[index] = _.pluck(array, index);
     }
-    return results;
+    return result;
   };
 
   // Converts lists into objects. Pass either a single array of `[key, value]`
@@ -530,9 +599,8 @@
   // pairs, or two parallel arrays of the same length -- one of keys, and one of
   // the corresponding values.
   _.object = function(list, values) {
-    if (list == null) return {};
     var result = {};
-    for (var i = 0, length = list.length; i < length; i++) {
+    for (var i = 0, length = getLength(list); i < length; i++) {
       if (values) {
         result[list[i]] = values[i];
       } else {
@@ -542,57 +610,83 @@
     return result;
   };
 
-  // If the browser doesn't supply us with indexOf (I'm looking at you, **MSIE**),
-  // we need this function. Return the position of the first occurrence of an
-  // item in an array, or -1 if the item is not included in the array.
-  // Delegates to **ECMAScript 5**'s native `indexOf` if available.
-  // If the array is large and already in sort order, pass `true`
-  // for **isSorted** to use binary search.
-  _.indexOf = function(array, item, isSorted) {
-    if (array == null) return -1;
-    var i = 0, length = array.length;
-    if (isSorted) {
-      if (typeof isSorted == 'number') {
-        i = (isSorted < 0 ? Math.max(0, length + isSorted) : isSorted);
-      } else {
-        i = _.sortedIndex(array, item);
-        return array[i] === item ? i : -1;
+  // Generator function to create the findIndex and findLastIndex functions
+  function createPredicateIndexFinder(dir) {
+    return function(array, predicate, context) {
+      predicate = cb(predicate, context);
+      var length = getLength(array);
+      var index = dir > 0 ? 0 : length - 1;
+      for (; index >= 0 && index < length; index += dir) {
+        if (predicate(array[index], index, array)) return index;
       }
-    }
-    if (nativeIndexOf && array.indexOf === nativeIndexOf) return array.indexOf(item, isSorted);
-    for (; i < length; i++) if (array[i] === item) return i;
-    return -1;
-  };
+      return -1;
+    };
+  }
 
-  // Delegates to **ECMAScript 5**'s native `lastIndexOf` if available.
-  _.lastIndexOf = function(array, item, from) {
-    if (array == null) return -1;
-    var hasIndex = from != null;
-    if (nativeLastIndexOf && array.lastIndexOf === nativeLastIndexOf) {
-      return hasIndex ? array.lastIndexOf(item, from) : array.lastIndexOf(item);
+  // Returns the first index on an array-like that passes a predicate test
+  _.findIndex = createPredicateIndexFinder(1);
+  _.findLastIndex = createPredicateIndexFinder(-1);
+
+  // Use a comparator function to figure out the smallest index at which
+  // an object should be inserted so as to maintain order. Uses binary search.
+  _.sortedIndex = function(array, obj, iteratee, context) {
+    iteratee = cb(iteratee, context, 1);
+    var value = iteratee(obj);
+    var low = 0, high = getLength(array);
+    while (low < high) {
+      var mid = Math.floor((low + high) / 2);
+      if (iteratee(array[mid]) < value) low = mid + 1; else high = mid;
     }
-    var i = (hasIndex ? from : array.length);
-    while (i--) if (array[i] === item) return i;
-    return -1;
+    return low;
   };
 
+  // Generator function to create the indexOf and lastIndexOf functions
+  function createIndexFinder(dir, predicateFind, sortedIndex) {
+    return function(array, item, idx) {
+      var i = 0, length = getLength(array);
+      if (typeof idx == 'number') {
+        if (dir > 0) {
+            i = idx >= 0 ? idx : Math.max(idx + length, i);
+        } else {
+            length = idx >= 0 ? Math.min(idx + 1, length) : idx + length + 1;
+        }
+      } else if (sortedIndex && idx && length) {
+        idx = sortedIndex(array, item);
+        return array[idx] === item ? idx : -1;
+      }
+      if (item !== item) {
+        idx = predicateFind(slice.call(array, i, length), _.isNaN);
+        return idx >= 0 ? idx + i : -1;
+      }
+      for (idx = dir > 0 ? i : length - 1; idx >= 0 && idx < length; idx += dir) {
+        if (array[idx] === item) return idx;
+      }
+      return -1;
+    };
+  }
+
+  // Return the position of the first occurrence of an item in an array,
+  // or -1 if the item is not included in the array.
+  // If the array is large and already in sort order, pass `true`
+  // for **isSorted** to use binary search.
+  _.indexOf = createIndexFinder(1, _.findIndex, _.sortedIndex);
+  _.lastIndexOf = createIndexFinder(-1, _.findLastIndex);
+
   // Generate an integer Array containing an arithmetic progression. A port of
   // the native Python `range()` function. See
   // [the Python documentation](http://docs.python.org/library/functions.html#range).
   _.range = function(start, stop, step) {
-    if (arguments.length <= 1) {
+    if (stop == null) {
       stop = start || 0;
       start = 0;
     }
-    step = arguments[2] || 1;
+    step = step || 1;
 
     var length = Math.max(Math.ceil((stop - start) / step), 0);
-    var idx = 0;
-    var range = new Array(length);
+    var range = Array(length);
 
-    while(idx < length) {
-      range[idx++] = start;
-      start += step;
+    for (var idx = 0; idx < length; idx++, start += step) {
+      range[idx] = start;
     }
 
     return range;
@@ -601,26 +695,27 @@
   // Function (ahem) Functions
   // ------------------
 
-  // Reusable constructor function for prototype setting.
-  var ctor = function(){};
+  // Determines whether to execute a function as a constructor
+  // or a normal function with the provided arguments
+  var executeBound = function(sourceFunc, boundFunc, context, callingContext, args) {
+    if (!(callingContext instanceof boundFunc)) return sourceFunc.apply(context, args);
+    var self = baseCreate(sourceFunc.prototype);
+    var result = sourceFunc.apply(self, args);
+    if (_.isObject(result)) return result;
+    return self;
+  };
 
   // Create a function bound to a given object (assigning `this`, and arguments,
   // optionally). Delegates to **ECMAScript 5**'s native `Function.bind` if
   // available.
   _.bind = function(func, context) {
-    var args, bound;
     if (nativeBind && func.bind === nativeBind) return nativeBind.apply(func, slice.call(arguments, 1));
-    if (!_.isFunction(func)) throw new TypeError;
-    args = slice.call(arguments, 2);
-    return bound = function() {
-      if (!(this instanceof bound)) return func.apply(context, args.concat(slice.call(arguments)));
-      ctor.prototype = func.prototype;
-      var self = new ctor;
-      ctor.prototype = null;
-      var result = func.apply(self, args.concat(slice.call(arguments)));
-      if (Object(result) === result) return result;
-      return self;
+    if (!_.isFunction(func)) throw new TypeError('Bind must be called on a function');
+    var args = slice.call(arguments, 2);
+    var bound = function() {
+      return executeBound(func, bound, context, this, args.concat(slice.call(arguments)));
     };
+    return bound;
   };
 
   // Partially apply a function by creating a version that has had some of its
@@ -628,15 +723,16 @@
   // as a placeholder, allowing any combination of arguments to be pre-filled.
   _.partial = function(func) {
     var boundArgs = slice.call(arguments, 1);
-    return function() {
-      var position = 0;
-      var args = boundArgs.slice();
-      for (var i = 0, length = args.length; i < length; i++) {
-        if (args[i] === _) args[i] = arguments[position++];
+    var bound = function() {
+      var position = 0, length = boundArgs.length;
+      var args = Array(length);
+      for (var i = 0; i < length; i++) {
+        args[i] = boundArgs[i] === _ ? arguments[position++] : boundArgs[i];
       }
       while (position < arguments.length) args.push(arguments[position++]);
-      return func.apply(this, args);
+      return executeBound(func, bound, this, this, args);
     };
+    return bound;
   };
 
   // Bind a number of an object's methods to that object. Remaining arguments
@@ -643,20 +739,25 @@
   // are the method names to be bound. Useful for ensuring that all callbacks
   // defined on an object belong to it.
   _.bindAll = function(obj) {
-    var funcs = slice.call(arguments, 1);
-    if (funcs.length === 0) throw new Error('bindAll must be passed function names');
-    each(funcs, function(f) { obj[f] = _.bind(obj[f], obj); });
+    var i, length = arguments.length, key;
+    if (length <= 1) throw new Error('bindAll must be passed function names');
+    for (i = 1; i < length; i++) {
+      key = arguments[i];
+      obj[key] = _.bind(obj[key], obj);
+    }
     return obj;
   };
 
   // Memoize an expensive function by storing its results.
   _.memoize = function(func, hasher) {
-    var memo = {};
-    hasher || (hasher = _.identity);
-    return function() {
-      var key = hasher.apply(this, arguments);
-      return _.has(memo, key) ? memo[key] : (memo[key] = func.apply(this, arguments));
+    var memoize = function(key) {
+      var cache = memoize.cache;
+      var address = '' + (hasher ? hasher.apply(this, arguments) : key);
+      if (!_.has(cache, address)) cache[address] = func.apply(this, arguments);
+      return cache[address];
     };
+    memoize.cache = {};
+    return memoize;
   };
 
   // Delays a function for the given number of milliseconds, and then calls
@@ -663,14 +764,14 @@
   // it with the arguments supplied.
   _.delay = function(func, wait) {
     var args = slice.call(arguments, 2);
-    return setTimeout(function(){ return func.apply(null, args); }, wait);
+    return setTimeout(function(){
+      return func.apply(null, args);
+    }, wait);
   };
 
   // Defers a function, scheduling it to run after the current call stack has
   // cleared.
-  _.defer = function(func) {
-    return _.delay.apply(_, [func, 1].concat(slice.call(arguments, 1)));
-  };
+  _.defer = _.partial(_.delay, _, 1);
 
   // Returns a function, that, when invoked, will only be triggered at most once
   // during a given window of time. Normally, the throttled function will run
@@ -681,12 +782,12 @@
     var context, args, result;
     var timeout = null;
     var previous = 0;
-    options || (options = {});
+    if (!options) options = {};
     var later = function() {
       previous = options.leading === false ? 0 : _.now();
       timeout = null;
       result = func.apply(context, args);
-      context = args = null;
+      if (!timeout) context = args = null;
     };
     return function() {
       var now = _.now();
@@ -694,12 +795,14 @@
       var remaining = wait - (now - previous);
       context = this;
       args = arguments;
-      if (remaining <= 0) {
-        clearTimeout(timeout);
-        timeout = null;
+      if (remaining <= 0 || remaining > wait) {
+        if (timeout) {
+          clearTimeout(timeout);
+          timeout = null;
+        }
         previous = now;
         result = func.apply(context, args);
-        context = args = null;
+        if (!timeout) context = args = null;
       } else if (!timeout && options.trailing !== false) {
         timeout = setTimeout(later, remaining);
       }
@@ -716,13 +819,14 @@
 
     var later = function() {
       var last = _.now() - timestamp;
-      if (last < wait) {
+
+      if (last < wait && last >= 0) {
         timeout = setTimeout(later, wait - last);
       } else {
         timeout = null;
         if (!immediate) {
           result = func.apply(context, args);
-          context = args = null;
+          if (!timeout) context = args = null;
         }
       }
     };
@@ -732,9 +836,7 @@
       args = arguments;
       timestamp = _.now();
       var callNow = immediate && !timeout;
-      if (!timeout) {
-        timeout = setTimeout(later, wait);
-      }
+      if (!timeout) timeout = setTimeout(later, wait);
       if (callNow) {
         result = func.apply(context, args);
         context = args = null;
@@ -744,19 +846,6 @@
     };
   };
 
-  // Returns a function that will be executed at most one time, no matter how
-  // often you call it. Useful for lazy initialization.
-  _.once = function(func) {
-    var ran = false, memo;
-    return function() {
-      if (ran) return memo;
-      ran = true;
-      memo = func.apply(this, arguments);
-      func = null;
-      return memo;
-    };
-  };
-
   // Returns the first function passed as an argument to the second,
   // allowing you to adjust arguments, run code before and after, and
   // conditionally execute the original function.
@@ -764,20 +853,27 @@
     return _.partial(wrapper, func);
   };
 
+  // Returns a negated version of the passed-in predicate.
+  _.negate = function(predicate) {
+    return function() {
+      return !predicate.apply(this, arguments);
+    };
+  };
+
   // Returns a function that is the composition of a list of functions, each
   // consuming the return value of the function that follows.
   _.compose = function() {
-    var funcs = arguments;
+    var args = arguments;
+    var start = args.length - 1;
     return function() {
-      var args = arguments;
-      for (var i = funcs.length - 1; i >= 0; i--) {
-        args = [funcs[i].apply(this, args)];
-      }
-      return args[0];
+      var i = start;
+      var result = args[start].apply(this, arguments);
+      while (i--) result = args[i].call(this, result);
+      return result;
     };
   };
 
-  // Returns a function that will only be executed after being called N times.
+  // Returns a function that will only be executed on and after the Nth call.
   _.after = function(times, func) {
     return function() {
       if (--times < 1) {
@@ -786,10 +882,48 @@
     };
   };
 
+  // Returns a function that will only be executed up to (but not including) the Nth call.
+  _.before = function(times, func) {
+    var memo;
+    return function() {
+      if (--times > 0) {
+        memo = func.apply(this, arguments);
+      }
+      if (times <= 1) func = null;
+      return memo;
+    };
+  };
+
+  // Returns a function that will be executed at most one time, no matter how
+  // often you call it. Useful for lazy initialization.
+  _.once = _.partial(_.before, 2);
+
   // Object Functions
   // ----------------
 
-  // Retrieve the names of an object's properties.
+  // Keys in IE < 9 that won't be iterated by `for key in ...` and thus missed.
+  var hasEnumBug = !{toString: null}.propertyIsEnumerable('toString');
+  var nonEnumerableProps = ['valueOf', 'isPrototypeOf', 'toString',
+                      'propertyIsEnumerable', 'hasOwnProperty', 'toLocaleString'];
+
+  function collectNonEnumProps(obj, keys) {
+    var nonEnumIdx = nonEnumerableProps.length;
+    var constructor = obj.constructor;
+    var proto = (_.isFunction(constructor) && constructor.prototype) || ObjProto;
+
+    // Constructor is a special case.
+    var prop = 'constructor';
+    if (_.has(obj, prop) && !_.contains(keys, prop)) keys.push(prop);
+
+    while (nonEnumIdx--) {
+      prop = nonEnumerableProps[nonEnumIdx];
+      if (prop in obj && obj[prop] !== proto[prop] && !_.contains(keys, prop)) {
+        keys.push(prop);
+      }
+    }
+  }
+
+  // Retrieve the names of an object's own properties.
   // Delegates to **ECMAScript 5**'s native `Object.keys`
   _.keys = function(obj) {
     if (!_.isObject(obj)) return [];
@@ -796,14 +930,26 @@
     if (nativeKeys) return nativeKeys(obj);
     var keys = [];
     for (var key in obj) if (_.has(obj, key)) keys.push(key);
+    // Ahem, IE < 9.
+    if (hasEnumBug) collectNonEnumProps(obj, keys);
     return keys;
   };
 
+  // Retrieve all the property names of an object.
+  _.allKeys = function(obj) {
+    if (!_.isObject(obj)) return [];
+    var keys = [];
+    for (var key in obj) keys.push(key);
+    // Ahem, IE < 9.
+    if (hasEnumBug) collectNonEnumProps(obj, keys);
+    return keys;
+  };
+
   // Retrieve the values of an object's properties.
   _.values = function(obj) {
     var keys = _.keys(obj);
     var length = keys.length;
-    var values = new Array(length);
+    var values = Array(length);
     for (var i = 0; i < length; i++) {
       values[i] = obj[keys[i]];
     }
@@ -810,11 +956,26 @@
     return values;
   };
 
+  // Returns the results of applying the iteratee to each element of the object
+  // In contrast to _.map it returns an object
+  _.mapObject = function(obj, iteratee, context) {
+    iteratee = cb(iteratee, context);
+    var keys =  _.keys(obj),
+          length = keys.length,
+          results = {},
+          currentKey;
+      for (var index = 0; index < length; index++) {
+        currentKey = keys[index];
+        results[currentKey] = iteratee(obj[currentKey], currentKey, obj);
+      }
+      return results;
+  };
+
   // Convert an object into a list of `[key, value]` pairs.
   _.pairs = function(obj) {
     var keys = _.keys(obj);
     var length = keys.length;
-    var pairs = new Array(length);
+    var pairs = Array(length);
     for (var i = 0; i < length; i++) {
       pairs[i] = [keys[i], obj[keys[i]]];
     }
@@ -842,47 +1003,65 @@
   };
 
   // Extend a given object with all the properties in passed-in object(s).
-  _.extend = function(obj) {
-    each(slice.call(arguments, 1), function(source) {
-      if (source) {
-        for (var prop in source) {
-          obj[prop] = source[prop];
-        }
-      }
-    });
-    return obj;
+  _.extend = createAssigner(_.allKeys);
+
+  // Assigns a given object with all the own properties in the passed-in object(s)
+  // (https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Object/assign)
+  _.extendOwn = _.assign = createAssigner(_.keys);
+
+  // Returns the first key on an object that passes a predicate test
+  _.findKey = function(obj, predicate, context) {
+    predicate = cb(predicate, context);
+    var keys = _.keys(obj), key;
+    for (var i = 0, length = keys.length; i < length; i++) {
+      key = keys[i];
+      if (predicate(obj[key], key, obj)) return key;
+    }
   };
 
   // Return a copy of the object only containing the whitelisted properties.
-  _.pick = function(obj) {
-    var copy = {};
-    var keys = concat.apply(ArrayProto, slice.call(arguments, 1));
-    each(keys, function(key) {
-      if (key in obj) copy[key] = obj[key];
-    });
-    return copy;
+  _.pick = function(object, oiteratee, context) {
+    var result = {}, obj = object, iteratee, keys;
+    if (obj == null) return result;
+    if (_.isFunction(oiteratee)) {
+      keys = _.allKeys(obj);
+      iteratee = optimizeCb(oiteratee, context);
+    } else {
+      keys = flatten(arguments, false, false, 1);
+      iteratee = function(value, key, obj) { return key in obj; };
+      obj = Object(obj);
+    }
+    for (var i = 0, length = keys.length; i < length; i++) {
+      var key = keys[i];
+      var value = obj[key];
+      if (iteratee(value, key, obj)) result[key] = value;
+    }
+    return result;
   };
 
    // Return a copy of the object without the blacklisted properties.
-  _.omit = function(obj) {
-    var copy = {};
-    var keys = concat.apply(ArrayProto, slice.call(arguments, 1));
-    for (var key in obj) {
-      if (!_.contains(keys, key)) copy[key] = obj[key];
+  _.omit = function(obj, iteratee, context) {
+    if (_.isFunction(iteratee)) {
+      iteratee = _.negate(iteratee);
+    } else {
+      var keys = _.map(flatten(arguments, false, false, 1), String);
+      iteratee = function(value, key) {
+        return !_.contains(keys, key);
+      };
     }
-    return copy;
+    return _.pick(obj, iteratee, context);
   };
 
   // Fill in a given object with default properties.
-  _.defaults = function(obj) {
-    each(slice.call(arguments, 1), function(source) {
-      if (source) {
-        for (var prop in source) {
-          if (obj[prop] === void 0) obj[prop] = source[prop];
-        }
-      }
-    });
-    return obj;
+  _.defaults = createAssigner(_.allKeys, true);
+
+  // Creates an object that inherits from the given prototype object.
+  // If additional properties are provided then they will be added to the
+  // created object.
+  _.create = function(prototype, props) {
+    var result = baseCreate(prototype);
+    if (props) _.extendOwn(result, props);
+    return result;
   };
 
   // Create a (shallow-cloned) duplicate of an object.
@@ -899,11 +1078,24 @@
     return obj;
   };
 
+  // Returns whether an object has a given set of `key:value` pairs.
+  _.isMatch = function(object, attrs) {
+    var keys = _.keys(attrs), length = keys.length;
+    if (object == null) return !length;
+    var obj = Object(object);
+    for (var i = 0; i < length; i++) {
+      var key = keys[i];
+      if (attrs[key] !== obj[key] || !(key in obj)) return false;
+    }
+    return true;
+  };
+
+
   // Internal recursive comparison function for `isEqual`.
   var eq = function(a, b, aStack, bStack) {
     // Identical objects are equal. `0 === -0`, but they aren't identical.
     // See the [Harmony `egal` proposal](http://wiki.ecmascript.org/doku.php?id=harmony:egal).
-    if (a === b) return a !== 0 || 1 / a == 1 / b;
+    if (a === b) return a !== 0 || 1 / a === 1 / b;
     // A strict comparison is necessary because `null == undefined`.
     if (a == null || b == null) return a === b;
     // Unwrap any wrapped objects.
@@ -911,89 +1103,90 @@
     if (b instanceof _) b = b._wrapped;
     // Compare `[[Class]]` names.
     var className = toString.call(a);
-    if (className != toString.call(b)) return false;
+    if (className !== toString.call(b)) return false;
     switch (className) {
-      // Strings, numbers, dates, and booleans are compared by value.
+      // Strings, numbers, regular expressions, dates, and booleans are compared by value.
+      case '[object RegExp]':
+      // RegExps are coerced to strings for comparison (Note: '' + /a/i === '/a/i')
       case '[object String]':
         // Primitives and their corresponding object wrappers are equivalent; thus, `"5"` is
         // equivalent to `new String("5")`.
-        return a == String(b);
+        return '' + a === '' + b;
       case '[object Number]':
-        // `NaN`s are equivalent, but non-reflexive. An `egal` comparison is performed for
-        // other numeric values.
-        return a != +a ? b != +b : (a == 0 ? 1 / a == 1 / b : a == +b);
+        // `NaN`s are equivalent, but non-reflexive.
+        // Object(NaN) is equivalent to NaN
+        if (+a !== +a) return +b !== +b;
+        // An `egal` comparison is performed for other numeric values.
+        return +a === 0 ? 1 / +a === 1 / b : +a === +b;
       case '[object Date]':
       case '[object Boolean]':
         // Coerce dates and booleans to numeric primitive values. Dates are compared by their
         // millisecond representations. Note that invalid dates with millisecond representations
         // of `NaN` are not equivalent.
-        return +a == +b;
-      // RegExps are compared by their source patterns and flags.
-      case '[object RegExp]':
-        return a.source == b.source &&
-               a.global == b.global &&
-               a.multiline == b.multiline &&
-               a.ignoreCase == b.ignoreCase;
+        return +a === +b;
     }
-    if (typeof a != 'object' || typeof b != 'object') return false;
+
+    var areArrays = className === '[object Array]';
+    if (!areArrays) {
+      if (typeof a != 'object' || typeof b != 'object') return false;
+
+      // Objects with different constructors are not equivalent, but `Object`s or `Array`s
+      // from different frames are.
+      var aCtor = a.constructor, bCtor = b.constructor;
+      if (aCtor !== bCtor && !(_.isFunction(aCtor) && aCtor instanceof aCtor &&
+                               _.isFunction(bCtor) && bCtor instanceof bCtor)
+                          && ('constructor' in a && 'constructor' in b)) {
+        return false;
+      }
+    }
     // Assume equality for cyclic structures. The algorithm for detecting cyclic
     // structures is adapted from ES 5.1 section 15.12.3, abstract operation `JO`.
+
+    // Initializing stack of traversed objects.
+    // It's done here since we only need them for objects and arrays comparison.
+    aStack = aStack || [];
+    bStack = bStack || [];
     var length = aStack.length;
     while (length--) {
       // Linear search. Performance is inversely proportional to the number of
       // unique nested structures.
-      if (aStack[length] == a) return bStack[length] == b;
+      if (aStack[length] === a) return bStack[length] === b;
     }
-    // Objects with different constructors are not equivalent, but `Object`s
-    // from different frames are.
-    var aCtor = a.constructor, bCtor = b.constructor;
-    if (aCtor !== bCtor && !(_.isFunction(aCtor) && (aCtor instanceof aCtor) &&
-                             _.isFunction(bCtor) && (bCtor instanceof bCtor))
-                        && ('constructor' in a && 'constructor' in b)) {
-      return false;
-    }
+
     // Add the first object to the stack of traversed objects.
     aStack.push(a);
     bStack.push(b);
-    var size = 0, result = true;
+
     // Recursively compare objects and arrays.
-    if (className == '[object Array]') {
+    if (areArrays) {
       // Compare array lengths to determine if a deep comparison is necessary.
-      size = a.length;
-      result = size == b.length;
-      if (result) {
-        // Deep compare the contents, ignoring non-numeric properties.
-        while (size--) {
-          if (!(result = eq(a[size], b[size], aStack, bStack))) break;
-        }
+      length = a.length;
+      if (length !== b.length) return false;
+      // Deep compare the contents, ignoring non-numeric properties.
+      while (length--) {
+        if (!eq(a[length], b[length], aStack, bStack)) return false;
       }
     } else {
       // Deep compare objects.
-      for (var key in a) {
-        if (_.has(a, key)) {
-          // Count the expected number of properties.
-          size++;
-          // Deep compare each member.
-          if (!(result = _.has(b, key) && eq(a[key], b[key], aStack, bStack))) break;
-        }
+      var keys = _.keys(a), key;
+      length = keys.length;
+      // Ensure that both objects contain the same number of properties before comparing deep equality.
+      if (_.keys(b).length !== length) return false;
+      while (length--) {
+        // Deep compare each member
+        key = keys[length];
+        if (!(_.has(b, key) && eq(a[key], b[key], aStack, bStack))) return false;
       }
-      // Ensure that both objects contain the same number of properties.
-      if (result) {
-        for (key in b) {
-          if (_.has(b, key) && !(size--)) break;
-        }
-        result = !size;
-      }
     }
     // Remove the first object from the stack of traversed objects.
     aStack.pop();
     bStack.pop();
-    return result;
+    return true;
   };
 
   // Perform a deep comparison to check if two objects are equal.
   _.isEqual = function(a, b) {
-    return eq(a, b, [], []);
+    return eq(a, b);
   };
 
   // Is a given array, string, or object empty?
@@ -1000,9 +1193,8 @@
   // An "empty" object has no enumerable own-properties.
   _.isEmpty = function(obj) {
     if (obj == null) return true;
-    if (_.isArray(obj) || _.isString(obj)) return obj.length === 0;
-    for (var key in obj) if (_.has(obj, key)) return false;
-    return true;
+    if (isArrayLike(obj) && (_.isArray(obj) || _.isString(obj) || _.isArguments(obj))) return obj.length === 0;
+    return _.keys(obj).length === 0;
   };
 
   // Is a given value a DOM element?
@@ -1013,33 +1205,35 @@
   // Is a given value an array?
   // Delegates to ECMA5's native Array.isArray
   _.isArray = nativeIsArray || function(obj) {
-    return toString.call(obj) == '[object Array]';
+    return toString.call(obj) === '[object Array]';
   };
 
   // Is a given variable an object?
   _.isObject = function(obj) {
-    return obj === Object(obj);
+    var type = typeof obj;
+    return type === 'function' || type === 'object' && !!obj;
   };
 
-  // Add some isType methods: isArguments, isFunction, isString, isNumber, isDate, isRegExp.
-  each(['Arguments', 'Function', 'String', 'Number', 'Date', 'RegExp'], function(name) {
+  // Add some isType methods: isArguments, isFunction, isString, isNumber, isDate, isRegExp, isError.
+  _.each(['Arguments', 'Function', 'String', 'Number', 'Date', 'RegExp', 'Error'], function(name) {
     _['is' + name] = function(obj) {
-      return toString.call(obj) == '[object ' + name + ']';
+      return toString.call(obj) === '[object ' + name + ']';
     };
   });
 
-  // Define a fallback version of the method in browsers (ahem, IE), where
+  // Define a fallback version of the method in browsers (ahem, IE < 9), where
   // there isn't any inspectable "Arguments" type.
   if (!_.isArguments(arguments)) {
     _.isArguments = function(obj) {
-      return !!(obj && _.has(obj, 'callee'));
+      return _.has(obj, 'callee');
     };
   }
 
-  // Optimize `isFunction` if appropriate.
-  if (typeof (/./) !== 'function') {
+  // Optimize `isFunction` if appropriate. Work around some typeof bugs in old v8,
+  // IE 11 (#1621), and in Safari 8 (#1929).
+  if (typeof /./ != 'function' && typeof Int8Array != 'object') {
     _.isFunction = function(obj) {
-      return typeof obj === 'function';
+      return typeof obj == 'function' || false;
     };
   }
 
@@ -1050,12 +1244,12 @@
 
   // Is the given value `NaN`? (NaN is the only number which does not equal itself).
   _.isNaN = function(obj) {
-    return _.isNumber(obj) && obj != +obj;
+    return _.isNumber(obj) && obj !== +obj;
   };
 
   // Is a given value a boolean?
   _.isBoolean = function(obj) {
-    return obj === true || obj === false || toString.call(obj) == '[object Boolean]';
+    return obj === true || obj === false || toString.call(obj) === '[object Boolean]';
   };
 
   // Is a given value equal to null?
@@ -1071,7 +1265,7 @@
   // Shortcut function for checking if an object has a given property directly
   // on itself (in other words, not on a prototype).
   _.has = function(obj, key) {
-    return hasOwnProperty.call(obj, key);
+    return obj != null && hasOwnProperty.call(obj, key);
   };
 
   // Utility Functions
@@ -1084,39 +1278,43 @@
     return this;
   };
 
-  // Keep the identity function around for default iterators.
+  // Keep the identity function around for default iteratees.
   _.identity = function(value) {
     return value;
   };
 
+  // Predicate-generating functions. Often useful outside of Underscore.
   _.constant = function(value) {
-    return function () {
+    return function() {
       return value;
     };
   };
 
-  _.property = function(key) {
-    return function(obj) {
+  _.noop = function(){};
+
+  _.property = property;
+
+  // Generates a function for a given object that returns a given property.
+  _.propertyOf = function(obj) {
+    return obj == null ? function(){} : function(key) {
       return obj[key];
     };
   };
 
-  // Returns a predicate for checking whether an object has a given set of `key:value` pairs.
-  _.matches = function(attrs) {
+  // Returns a predicate for checking whether an object has a given set of
+  // `key:value` pairs.
+  _.matcher = _.matches = function(attrs) {
+    attrs = _.extendOwn({}, attrs);
     return function(obj) {
-      if (obj === attrs) return true; //avoid comparing an object to itself.
-      for (var key in attrs) {
-        if (attrs[key] !== obj[key])
-          return false;
-      }
-      return true;
-    }
+      return _.isMatch(obj, attrs);
+    };
   };
 
   // Run a function **n** times.
-  _.times = function(n, iterator, context) {
+  _.times = function(n, iteratee, context) {
     var accum = Array(Math.max(0, n));
-    for (var i = 0; i < n; i++) accum[i] = iterator.call(context, i);
+    iteratee = optimizeCb(iteratee, context, 1);
+    for (var i = 0; i < n; i++) accum[i] = iteratee(i);
     return accum;
   };
 
@@ -1130,56 +1328,48 @@
   };
 
   // A (possibly faster) way to get the current timestamp as an integer.
-  _.now = Date.now || function() { return new Date().getTime(); };
-
-  // List of HTML entities for escaping.
-  var entityMap = {
-    escape: {
-      '&': '&amp;',
-      '<': '&lt;',
-      '>': '&gt;',
-      '"': '&quot;',
-      "'": '&#x27;'
-    }
+  _.now = Date.now || function() {
+    return new Date().getTime();
   };
-  entityMap.unescape = _.invert(entityMap.escape);
 
-  // Regexes containing the keys and values listed immediately above.
-  var entityRegexes = {
-    escape:   new RegExp('[' + _.keys(entityMap.escape).join('') + ']', 'g'),
-    unescape: new RegExp('(' + _.keys(entityMap.unescape).join('|') + ')', 'g')
+   // List of HTML entities for escaping.
+  var escapeMap = {
+    '&': '&amp;',
+    '<': '&lt;',
+    '>': '&gt;',
+    '"': '&quot;',
+    "'": '&#x27;',
+    '`': '&#x60;'
   };
+  var unescapeMap = _.invert(escapeMap);
 
   // Functions for escaping and unescaping strings to/from HTML interpolation.
-  _.each(['escape', 'unescape'], function(method) {
-    _[method] = function(string) {
-      if (string == null) return '';
-      return ('' + string).replace(entityRegexes[method], function(match) {
-        return entityMap[method][match];
-      });
+  var createEscaper = function(map) {
+    var escaper = function(match) {
+      return map[match];
     };
-  });
+    // Regexes for identifying a key that needs to be escaped
+    var source = '(?:' + _.keys(map).join('|') + ')';
+    var testRegexp = RegExp(source);
+    var replaceRegexp = RegExp(source, 'g');
+    return function(string) {
+      string = string == null ? '' : '' + string;
+      return testRegexp.test(string) ? string.replace(replaceRegexp, escaper) : string;
+    };
+  };
+  _.escape = createEscaper(escapeMap);
+  _.unescape = createEscaper(unescapeMap);
 
   // If the value of the named `property` is a function then invoke it with the
   // `object` as context; otherwise, return it.
-  _.result = function(object, property) {
-    if (object == null) return void 0;
-    var value = object[property];
+  _.result = function(object, property, fallback) {
+    var value = object == null ? void 0 : object[property];
+    if (value === void 0) {
+      value = fallback;
+    }
     return _.isFunction(value) ? value.call(object) : value;
   };
 
-  // Add your own custom functions to the Underscore object.
-  _.mixin = function(obj) {
-    each(_.functions(obj), function(name) {
-      var func = _[name] = obj[name];
-      _.prototype[name] = function() {
-        var args = [this._wrapped];
-        push.apply(args, arguments);
-        return result.call(this, func.apply(_, args));
-      };
-    });
-  };
-
   // Generate a unique integer id (unique within the entire client session).
   // Useful for temporary DOM ids.
   var idCounter = 0;
@@ -1208,22 +1398,26 @@
     '\\':     '\\',
     '\r':     'r',
     '\n':     'n',
-    '\t':     't',
     '\u2028': 'u2028',
     '\u2029': 'u2029'
   };
 
-  var escaper = /\\|'|\r|\n|\t|\u2028|\u2029/g;
+  var escaper = /\\|'|\r|\n|\u2028|\u2029/g;
 
+  var escapeChar = function(match) {
+    return '\\' + escapes[match];
+  };
+
   // JavaScript micro-templating, similar to John Resig's implementation.
   // Underscore templating handles arbitrary delimiters, preserves whitespace,
   // and correctly escapes quotes within interpolated code.
-  _.template = function(text, data, settings) {
-    var render;
+  // NB: `oldSettings` only exists for backwards compatibility.
+  _.template = function(text, settings, oldSettings) {
+    if (!settings && oldSettings) settings = oldSettings;
     settings = _.defaults({}, settings, _.templateSettings);
 
     // Combine delimiters into one regular expression via alternation.
-    var matcher = new RegExp([
+    var matcher = RegExp([
       (settings.escape || noMatch).source,
       (settings.interpolate || noMatch).source,
       (settings.evaluate || noMatch).source
@@ -1233,19 +1427,18 @@
     var index = 0;
     var source = "__p+='";
     text.replace(matcher, function(match, escape, interpolate, evaluate, offset) {
-      source += text.slice(index, offset)
-        .replace(escaper, function(match) { return '\\' + escapes[match]; });
+      source += text.slice(index, offset).replace(escaper, escapeChar);
+      index = offset + match.length;
 
       if (escape) {
         source += "'+\n((__t=(" + escape + "))==null?'':_.escape(__t))+\n'";
-      }
-      if (interpolate) {
+      } else if (interpolate) {
         source += "'+\n((__t=(" + interpolate + "))==null?'':__t)+\n'";
-      }
-      if (evaluate) {
+      } else if (evaluate) {
         source += "';\n" + evaluate + "\n__p+='";
       }
-      index = offset + match.length;
+
+      // Adobe VMs need the match returned to produce the correct offest.
       return match;
     });
     source += "';\n";
@@ -1255,29 +1448,31 @@
 
     source = "var __t,__p='',__j=Array.prototype.join," +
       "print=function(){__p+=__j.call(arguments,'');};\n" +
-      source + "return __p;\n";
+      source + 'return __p;\n';
 
     try {
-      render = new Function(settings.variable || 'obj', '_', source);
+      var render = new Function(settings.variable || 'obj', '_', source);
     } catch (e) {
       e.source = source;
       throw e;
     }
 
-    if (data) return render(data, _);
     var template = function(data) {
       return render.call(this, data, _);
     };
 
-    // Provide the compiled function source as a convenience for precompilation.
-    template.source = 'function(' + (settings.variable || 'obj') + '){\n' + source + '}';
+    // Provide the compiled source as a convenience for precompilation.
+    var argument = settings.variable || 'obj';
+    template.source = 'function(' + argument + '){\n' + source + '}';
 
     return template;
   };
 
-  // Add a "chain" function, which will delegate to the wrapper.
+  // Add a "chain" function. Start chaining a wrapped Underscore object.
   _.chain = function(obj) {
-    return _(obj).chain();
+    var instance = _(obj);
+    instance._chain = true;
+    return instance;
   };
 
   // OOP
@@ -1287,47 +1482,57 @@
   // underscore functions. Wrapped objects may be chained.
 
   // Helper function to continue chaining intermediate results.
-  var result = function(obj) {
-    return this._chain ? _(obj).chain() : obj;
+  var result = function(instance, obj) {
+    return instance._chain ? _(obj).chain() : obj;
   };
 
+  // Add your own custom functions to the Underscore object.
+  _.mixin = function(obj) {
+    _.each(_.functions(obj), function(name) {
+      var func = _[name] = obj[name];
+      _.prototype[name] = function() {
+        var args = [this._wrapped];
+        push.apply(args, arguments);
+        return result(this, func.apply(_, args));
+      };
+    });
+  };
+
   // Add all of the Underscore functions to the wrapper object.
   _.mixin(_);
 
   // Add all mutator Array functions to the wrapper.
-  each(['pop', 'push', 'reverse', 'shift', 'sort', 'splice', 'unshift'], function(name) {
+  _.each(['pop', 'push', 'reverse', 'shift', 'sort', 'splice', 'unshift'], function(name) {
     var method = ArrayProto[name];
     _.prototype[name] = function() {
       var obj = this._wrapped;
       method.apply(obj, arguments);
-      if ((name == 'shift' || name == 'splice') && obj.length === 0) delete obj[0];
-      return result.call(this, obj);
+      if ((name === 'shift' || name === 'splice') && obj.length === 0) delete obj[0];
+      return result(this, obj);
     };
   });
 
   // Add all accessor Array functions to the wrapper.
-  each(['concat', 'join', 'slice'], function(name) {
+  _.each(['concat', 'join', 'slice'], function(name) {
     var method = ArrayProto[name];
     _.prototype[name] = function() {
-      return result.call(this, method.apply(this._wrapped, arguments));
+      return result(this, method.apply(this._wrapped, arguments));
     };
   });
 
-  _.extend(_.prototype, {
+  // Extracts the result from a wrapped and chained object.
+  _.prototype.value = function() {
+    return this._wrapped;
+  };
 
-    // Start chaining a wrapped Underscore object.
-    chain: function() {
-      this._chain = true;
-      return this;
-    },
+  // Provide unwrapping proxy for some methods used in engine operations
+  // such as arithmetic and JSON stringification.
+  _.prototype.valueOf = _.prototype.toJSON = _.prototype.value;
 
-    // Extracts the result from a wrapped and chained object.
-    value: function() {
-      return this._wrapped;
-    }
+  _.prototype.toString = function() {
+    return '' + this._wrapped;
+  };
 
-  });
-
   // AMD registration happens at the end for compatibility with AMD loaders
   // that may not enforce next-turn semantics on modules. Even though general
   // practice for AMD registration is to be anonymous, underscore registers
@@ -1340,4 +1545,4 @@
       return _;
     });
   }
-}).call(this);
+}.call(this));
Index: src/wp-includes/js/underscore.min.js
===================================================================
--- src/wp-includes/js/underscore.min.js	(revision 36320)
+++ src/wp-includes/js/underscore.min.js	(working copy)
@@ -1,5 +1,5 @@
-//     Underscore.js 1.6.0
+//     Underscore.js 1.8.3
 //     http://underscorejs.org
-//     (c) 2009-2014 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
+//     (c) 2009-2015 Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
 //     Underscore may be freely distributed under the MIT license.
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