diff -r 000000000000 -r 6474c204b198 browser/devtools/shared/widgets/ViewHelpers.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/shared/widgets/ViewHelpers.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,1681 @@
+/* -*- Mode: javascript; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ft=javascript ts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+const Cu = Components.utils;
+
+const PANE_APPEARANCE_DELAY = 50;
+const PAGE_SIZE_ITEM_COUNT_RATIO = 5;
+const WIDGET_FOCUSABLE_NODES = new Set(["vbox", "hbox"]);
+
+Cu.import("resource://gre/modules/Services.jsm");
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+Cu.import("resource://gre/modules/Timer.jsm");
+Cu.import("resource://gre/modules/devtools/DevToolsUtils.jsm");
+
+this.EXPORTED_SYMBOLS = [
+  "Heritage", "ViewHelpers", "WidgetMethods",
+  "setNamedTimeout", "clearNamedTimeout",
+  "setConditionalTimeout", "clearConditionalTimeout",
+];
+
+/**
+ * Inheritance helpers from the addon SDK's core/heritage.
+ * Remove these when all devtools are loadered.
+ */
+this.Heritage = {
+  /**
+   * @see extend in sdk/core/heritage.
+   */
+  extend: function(aPrototype, aProperties = {}) {
+    return Object.create(aPrototype, this.getOwnPropertyDescriptors(aProperties));
+  },
+
+  /**
+   * @see getOwnPropertyDescriptors in sdk/core/heritage.
+   */
+  getOwnPropertyDescriptors: function(aObject) {
+    return Object.getOwnPropertyNames(aObject).reduce((aDescriptor, aName) => {
+      aDescriptor[aName] = Object.getOwnPropertyDescriptor(aObject, aName);
+      return aDescriptor;
+    }, {});
+  }
+};
+
+/**
+ * Helper for draining a rapid succession of events and invoking a callback
+ * once everything settles down.
+ *
+ * @param string aId
+ *        A string identifier for the named timeout.
+ * @param number aWait
+ *        The amount of milliseconds to wait after no more events are fired.
+ * @param function aCallback
+ *        Invoked when no more events are fired after the specified time.
+ */
+this.setNamedTimeout = function setNamedTimeout(aId, aWait, aCallback) {
+  clearNamedTimeout(aId);
+
+  namedTimeoutsStore.set(aId, setTimeout(() =>
+    namedTimeoutsStore.delete(aId) && aCallback(), aWait));
+};
+
+/**
+ * Clears a named timeout.
+ * @see setNamedTimeout
+ *
+ * @param string aId
+ *        A string identifier for the named timeout.
+ */
+this.clearNamedTimeout = function clearNamedTimeout(aId) {
+  if (!namedTimeoutsStore) {
+    return;
+  }
+  clearTimeout(namedTimeoutsStore.get(aId));
+  namedTimeoutsStore.delete(aId);
+};
+
+/**
+ * Same as `setNamedTimeout`, but invokes the callback only if the provided
+ * predicate function returns true. Otherwise, the timeout is re-triggered.
+ *
+ * @param string aId
+ *        A string identifier for the conditional timeout.
+ * @param number aWait
+ *        The amount of milliseconds to wait after no more events are fired.
+ * @param function aPredicate
+ *        The predicate function used to determine whether the timeout restarts.
+ * @param function aCallback
+ *        Invoked when no more events are fired after the specified time, and
+ *        the provided predicate function returns true.
+ */
+this.setConditionalTimeout = function setConditionalTimeout(aId, aWait, aPredicate, aCallback) {
+  setNamedTimeout(aId, aWait, function maybeCallback() {
+    if (aPredicate()) {
+      aCallback();
+      return;
+    }
+    setConditionalTimeout(aId, aWait, aPredicate, aCallback);
+  });
+};
+
+/**
+ * Clears a conditional timeout.
+ * @see setConditionalTimeout
+ *
+ * @param string aId
+ *        A string identifier for the conditional timeout.
+ */
+this.clearConditionalTimeout = function clearConditionalTimeout(aId) {
+  clearNamedTimeout(aId);
+};
+
+XPCOMUtils.defineLazyGetter(this, "namedTimeoutsStore", () => new Map());
+
+/**
+ * Helpers for creating and messaging between UI components.
+ */
+this.ViewHelpers = {
+  /**
+   * Convenience method, dispatching a custom event.
+   *
+   * @param nsIDOMNode aTarget
+   *        A custom target element to dispatch the event from.
+   * @param string aType
+   *        The name of the event.
+   * @param any aDetail
+   *        The data passed when initializing the event.
+   * @return boolean
+   *         True if the event was cancelled or a registered handler
+   *         called preventDefault.
+   */
+  dispatchEvent: function(aTarget, aType, aDetail) {
+    if (!(aTarget instanceof Ci.nsIDOMNode)) {
+      return true; // Event cancelled.
+    }
+    let document = aTarget.ownerDocument || aTarget;
+    let dispatcher = aTarget.ownerDocument ? aTarget : document.documentElement;
+
+    let event = document.createEvent("CustomEvent");
+    event.initCustomEvent(aType, true, true, aDetail);
+    return dispatcher.dispatchEvent(event);
+  },
+
+  /**
+   * Helper delegating some of the DOM attribute methods of a node to a widget.
+   *
+   * @param object aWidget
+   *        The widget to assign the methods to.
+   * @param nsIDOMNode aNode
+   *        A node to delegate the methods to.
+   */
+  delegateWidgetAttributeMethods: function(aWidget, aNode) {
+    aWidget.getAttribute =
+      aWidget.getAttribute || aNode.getAttribute.bind(aNode);
+    aWidget.setAttribute =
+      aWidget.setAttribute || aNode.setAttribute.bind(aNode);
+    aWidget.removeAttribute =
+      aWidget.removeAttribute || aNode.removeAttribute.bind(aNode);
+  },
+
+  /**
+   * Helper delegating some of the DOM event methods of a node to a widget.
+   *
+   * @param object aWidget
+   *        The widget to assign the methods to.
+   * @param nsIDOMNode aNode
+   *        A node to delegate the methods to.
+   */
+  delegateWidgetEventMethods: function(aWidget, aNode) {
+    aWidget.addEventListener =
+      aWidget.addEventListener || aNode.addEventListener.bind(aNode);
+    aWidget.removeEventListener =
+      aWidget.removeEventListener || aNode.removeEventListener.bind(aNode);
+  },
+
+  /**
+   * Checks if the specified object looks like it's been decorated by an
+   * event emitter.
+   *
+   * @return boolean
+   *         True if it looks, walks and quacks like an event emitter.
+   */
+  isEventEmitter: function(aObject) {
+    return aObject && aObject.on && aObject.off && aObject.once && aObject.emit;
+  },
+
+  /**
+   * Checks if the specified object is an instance of a DOM node.
+   *
+   * @return boolean
+   *         True if it's a node, false otherwise.
+   */
+  isNode: function(aObject) {
+    return aObject instanceof Ci.nsIDOMNode ||
+           aObject instanceof Ci.nsIDOMElement ||
+           aObject instanceof Ci.nsIDOMDocumentFragment;
+  },
+
+  /**
+   * Prevents event propagation when navigation keys are pressed.
+   *
+   * @param Event e
+   *        The event to be prevented.
+   */
+  preventScrolling: function(e) {
+    switch (e.keyCode) {
+      case e.DOM_VK_UP:
+      case e.DOM_VK_DOWN:
+      case e.DOM_VK_LEFT:
+      case e.DOM_VK_RIGHT:
+      case e.DOM_VK_PAGE_UP:
+      case e.DOM_VK_PAGE_DOWN:
+      case e.DOM_VK_HOME:
+      case e.DOM_VK_END:
+        e.preventDefault();
+        e.stopPropagation();
+    }
+  },
+
+  /**
+   * Sets a side pane hidden or visible.
+   *
+   * @param object aFlags
+   *        An object containing some of the following properties:
+   *        - visible: true if the pane should be shown, false to hide
+   *        - animated: true to display an animation on toggle
+   *        - delayed: true to wait a few cycles before toggle
+   *        - callback: a function to invoke when the toggle finishes
+   * @param nsIDOMNode aPane
+   *        The element representing the pane to toggle.
+   */
+  togglePane: function(aFlags, aPane) {
+    // Make sure a pane is actually available first.
+    if (!aPane) {
+      return;
+    }
+
+    // Hiding is always handled via margins, not the hidden attribute.
+    aPane.removeAttribute("hidden");
+
+    // Add a class to the pane to handle min-widths, margins and animations.
+    if (!aPane.classList.contains("generic-toggled-side-pane")) {
+      aPane.classList.add("generic-toggled-side-pane");
+    }
+
+    // Avoid useless toggles.
+    if (aFlags.visible == !aPane.hasAttribute("pane-collapsed")) {
+      if (aFlags.callback) aFlags.callback();
+      return;
+    }
+
+    // The "animated" attributes enables animated toggles (slide in-out).
+    if (aFlags.animated) {
+      aPane.setAttribute("animated", "");
+    } else {
+      aPane.removeAttribute("animated");
+    }
+
+    // Computes and sets the pane margins in order to hide or show it.
+    let doToggle = () => {
+      if (aFlags.visible) {
+        aPane.style.marginLeft = "0";
+        aPane.style.marginRight = "0";
+        aPane.removeAttribute("pane-collapsed");
+      } else {
+        let margin = ~~(aPane.getAttribute("width")) + 1;
+        aPane.style.marginLeft = -margin + "px";
+        aPane.style.marginRight = -margin + "px";
+        aPane.setAttribute("pane-collapsed", "");
+      }
+
+      // Invoke the callback when the transition ended.
+      if (aFlags.animated) {
+        aPane.addEventListener("transitionend", function onEvent() {
+          aPane.removeEventListener("transitionend", onEvent, false);
+          if (aFlags.callback) aFlags.callback();
+        }, false);
+      }
+      // Invoke the callback immediately since there's no transition.
+      else {
+        if (aFlags.callback) aFlags.callback();
+      }
+    }
+
+    // Sometimes it's useful delaying the toggle a few ticks to ensure
+    // a smoother slide in-out animation.
+    if (aFlags.delayed) {
+      aPane.ownerDocument.defaultView.setTimeout(doToggle, PANE_APPEARANCE_DELAY);
+    } else {
+      doToggle();
+    }
+  }
+};
+
+/**
+ * Localization convenience methods.
+ *
+ * @param string aStringBundleName
+ *        The desired string bundle's name.
+ */
+ViewHelpers.L10N = function(aStringBundleName) {
+  XPCOMUtils.defineLazyGetter(this, "stringBundle", () =>
+    Services.strings.createBundle(aStringBundleName));
+
+  XPCOMUtils.defineLazyGetter(this, "ellipsis", () =>
+    Services.prefs.getComplexValue("intl.ellipsis", Ci.nsIPrefLocalizedString).data);
+};
+
+ViewHelpers.L10N.prototype = {
+  stringBundle: null,
+
+  /**
+   * L10N shortcut function.
+   *
+   * @param string aName
+   * @return string
+   */
+  getStr: function(aName) {
+    return this.stringBundle.GetStringFromName(aName);
+  },
+
+  /**
+   * L10N shortcut function.
+   *
+   * @param string aName
+   * @param array aArgs
+   * @return string
+   */
+  getFormatStr: function(aName, ...aArgs) {
+    return this.stringBundle.formatStringFromName(aName, aArgs, aArgs.length);
+  },
+
+  /**
+   * L10N shortcut function for numeric arguments that need to be formatted.
+   * All numeric arguments will be fixed to 2 decimals and given a localized
+   * decimal separator. Other arguments will be left alone.
+   *
+   * @param string aName
+   * @param array aArgs
+   * @return string
+   */
+  getFormatStrWithNumbers: function(aName, ...aArgs) {
+    let newArgs = aArgs.map(x => typeof x == "number" ? this.numberWithDecimals(x, 2) : x);
+    return this.stringBundle.formatStringFromName(aName, newArgs, newArgs.length);
+  },
+
+  /**
+   * Converts a number to a locale-aware string format and keeps a certain
+   * number of decimals.
+   *
+   * @param number aNumber
+   *        The number to convert.
+   * @param number aDecimals [optional]
+   *        Total decimals to keep.
+   * @return string
+   *         The localized number as a string.
+   */
+  numberWithDecimals: function(aNumber, aDecimals = 0) {
+    // If this is an integer, don't do anything special.
+    if (aNumber == (aNumber | 0)) {
+      return aNumber;
+    }
+    // Remove {n} trailing decimals. Can't use toFixed(n) because
+    // toLocaleString converts the number to a string. Also can't use
+    // toLocaleString(, { maximumFractionDigits: n }) because it's not
+    // implemented on OS X (bug 368838). Gross.
+    let localized = aNumber.toLocaleString(); // localize
+    let padded = localized + new Array(aDecimals).join("0"); // pad with zeros
+    let match = padded.match("([^]*?\\d{" + aDecimals + "})\\d*$");
+    return match.pop();
+  }
+};
+
+/**
+ * Shortcuts for lazily accessing and setting various preferences.
+ * Usage:
+ *   let prefs = new ViewHelpers.Prefs("root.path.to.branch", {
+ *     myIntPref: ["Int", "leaf.path.to.my-int-pref"],
+ *     myCharPref: ["Char", "leaf.path.to.my-char-pref"],
+ *     ...
+ *   });
+ *
+ *   prefs.myCharPref = "foo";
+ *   let aux = prefs.myCharPref;
+ *
+ * @param string aPrefsRoot
+ *        The root path to the required preferences branch.
+ * @param object aPrefsObject
+ *        An object containing { accessorName: [prefType, prefName] } keys.
+ */
+ViewHelpers.Prefs = function(aPrefsRoot = "", aPrefsObject = {}) {
+  this.root = aPrefsRoot;
+
+  for (let accessorName in aPrefsObject) {
+    let [prefType, prefName] = aPrefsObject[accessorName];
+    this.map(accessorName, prefType, prefName);
+  }
+};
+
+ViewHelpers.Prefs.prototype = {
+  /**
+   * Helper method for getting a pref value.
+   *
+   * @param string aType
+   * @param string aPrefName
+   * @return any
+   */
+  _get: function(aType, aPrefName) {
+    if (this[aPrefName] === undefined) {
+      this[aPrefName] = Services.prefs["get" + aType + "Pref"](aPrefName);
+    }
+    return this[aPrefName];
+  },
+
+  /**
+   * Helper method for setting a pref value.
+   *
+   * @param string aType
+   * @param string aPrefName
+   * @param any aValue
+   */
+  _set: function(aType, aPrefName, aValue) {
+    Services.prefs["set" + aType + "Pref"](aPrefName, aValue);
+    this[aPrefName] = aValue;
+  },
+
+  /**
+   * Maps a property name to a pref, defining lazy getters and setters.
+   * Supported types are "Bool", "Char", "Int" and "Json" (which is basically
+   * just sugar for "Char" using the standard JSON serializer).
+   *
+   * @param string aAccessorName
+   * @param string aType
+   * @param string aPrefName
+   * @param array aSerializer
+   */
+  map: function(aAccessorName, aType, aPrefName, aSerializer = { in: e => e, out: e => e }) {
+    if (aType == "Json") {
+      this.map(aAccessorName, "Char", aPrefName, { in: JSON.parse, out: JSON.stringify });
+      return;
+    }
+
+    Object.defineProperty(this, aAccessorName, {
+      get: () => aSerializer.in(this._get(aType, [this.root, aPrefName].join("."))),
+      set: (e) => this._set(aType, [this.root, aPrefName].join("."), aSerializer.out(e))
+    });
+  }
+};
+
+/**
+ * A generic Item is used to describe children present in a Widget.
+ *
+ * This is basically a very thin wrapper around an nsIDOMNode, with a few
+ * characteristics, like a `value` and an `attachment`.
+ *
+ * The characteristics are optional, and their meaning is entirely up to you.
+ * - The `value` should be a string, passed as an argument.
+ * - The `attachment` is any kind of primitive or object, passed as an argument.
+ *
+ * Iterable via "for (let childItem of parentItem) { }".
+ *
+ * @param object aOwnerView
+ *        The owner view creating this item.
+ * @param nsIDOMNode aElement
+ *        A prebuilt node to be wrapped.
+ * @param string aValue
+ *        A string identifying the node.
+ * @param any aAttachment
+ *        Some attached primitive/object.
+ */
+function Item(aOwnerView, aElement, aValue, aAttachment) {
+  this.ownerView = aOwnerView;
+  this.attachment = aAttachment;
+  this._value = aValue + "";
+  this._prebuiltNode = aElement;
+};
+
+Item.prototype = {
+  get value() { return this._value; },
+  get target() { return this._target; },
+
+  /**
+   * Immediately appends a child item to this item.
+   *
+   * @param nsIDOMNode aElement
+   *        An nsIDOMNode representing the child element to append.
+   * @param object aOptions [optional]
+   *        Additional options or flags supported by this operation:
+   *          - attachment: some attached primitive/object for the item
+   *          - attributes: a batch of attributes set to the displayed element
+   *          - finalize: function invoked when the child item is removed
+   * @return Item
+   *         The item associated with the displayed element.
+   */
+  append: function(aElement, aOptions = {}) {
+    let item = new Item(this, aElement, "", aOptions.attachment);
+
+    // Entangle the item with the newly inserted child node.
+    // Make sure this is done with the value returned by appendChild(),
+    // to avoid storing a potential DocumentFragment.
+    this._entangleItem(item, this._target.appendChild(aElement));
+
+    // Handle any additional options after entangling the item.
+    if (aOptions.attributes) {
+      aOptions.attributes.forEach(e => item._target.setAttribute(e[0], e[1]));
+    }
+    if (aOptions.finalize) {
+      item.finalize = aOptions.finalize;
+    }
+
+    // Return the item associated with the displayed element.
+    return item;
+  },
+
+  /**
+   * Immediately removes the specified child item from this item.
+   *
+   * @param Item aItem
+   *        The item associated with the element to remove.
+   */
+  remove: function(aItem) {
+    if (!aItem) {
+      return;
+    }
+    this._target.removeChild(aItem._target);
+    this._untangleItem(aItem);
+  },
+
+  /**
+   * Entangles an item (model) with a displayed node element (view).
+   *
+   * @param Item aItem
+   *        The item describing a target element.
+   * @param nsIDOMNode aElement
+   *        The element displaying the item.
+   */
+  _entangleItem: function(aItem, aElement) {
+    this._itemsByElement.set(aElement, aItem);
+    aItem._target = aElement;
+  },
+
+  /**
+   * Untangles an item (model) from a displayed node element (view).
+   *
+   * @param Item aItem
+   *        The item describing a target element.
+   */
+  _untangleItem: function(aItem) {
+    if (aItem.finalize) {
+      aItem.finalize(aItem);
+    }
+    for (let childItem of aItem) {
+      aItem.remove(childItem);
+    }
+
+    this._unlinkItem(aItem);
+    aItem._target = null;
+  },
+
+  /**
+   * Deletes an item from the its parent's storage maps.
+   *
+   * @param Item aItem
+   *        The item describing a target element.
+   */
+  _unlinkItem: function(aItem) {
+    this._itemsByElement.delete(aItem._target);
+  },
+
+  /**
+   * Returns a string representing the object.
+   * @return string
+   */
+  toString: function() {
+    return this._value + " :: " + this._target + " :: " + this.attachment;
+  },
+
+  _value: "",
+  _target: null,
+  _prebuiltNode: null,
+  finalize: null,
+  attachment: null
+};
+
+// Creating maps thousands of times for widgets with a large number of children
+// fills up a lot of memory. Make sure these are instantiated only if needed.
+DevToolsUtils.defineLazyPrototypeGetter(Item.prototype, "_itemsByElement", Map);
+
+/**
+ * Some generic Widget methods handling Item instances.
+ * Iterable via "for (let childItem of wrappedView) { }".
+ *
+ * Usage:
+ *   function MyView() {
+ *     this.widget = new MyWidget(document.querySelector(".my-node"));
+ *   }
+ *
+ *   MyView.prototype = Heritage.extend(WidgetMethods, {
+ *     myMethod: function() {},
+ *     ...
+ *   });
+ *
+ * See https://gist.github.com/victorporof/5749386 for more details.
+ * The devtools/shared/widgets/SimpleListWidget.jsm is an implementation example.
+ *
+ * Language:
+ *   - An "item" is an instance of an Item.
+ *   - An "element" or "node" is a nsIDOMNode.
+ *
+ * The supplied widget can be any object implementing the following methods:
+ *   - function:nsIDOMNode insertItemAt(aIndex:number, aNode:nsIDOMNode, aValue:string)
+ *   - function:nsIDOMNode getItemAtIndex(aIndex:number)
+ *   - function removeChild(aChild:nsIDOMNode)
+ *   - function removeAllItems()
+ *   - get:nsIDOMNode selectedItem()
+ *   - set selectedItem(aChild:nsIDOMNode)
+ *   - function getAttribute(aName:string)
+ *   - function setAttribute(aName:string, aValue:string)
+ *   - function removeAttribute(aName:string)
+ *   - function addEventListener(aName:string, aCallback:function, aBubbleFlag:boolean)
+ *   - function removeEventListener(aName:string, aCallback:function, aBubbleFlag:boolean)
+ *
+ * Optional methods that can be implemented by the widget:
+ *   - function ensureElementIsVisible(aChild:nsIDOMNode)
+ *
+ * Optional attributes that may be handled (when calling get/set/removeAttribute):
+ *   - "emptyText": label temporarily added when there are no items present
+ *   - "headerText": label permanently added as a header
+ *
+ * For automagical keyboard and mouse accessibility, the widget should be an
+ * event emitter with the following events:
+ *   - "keyPress" -> (aName:string, aEvent:KeyboardEvent)
+ *   - "mousePress" -> (aName:string, aEvent:MouseEvent)
+ */
+this.WidgetMethods = {
+  /**
+   * Sets the element node or widget associated with this container.
+   * @param nsIDOMNode | object aWidget
+   */
+  set widget(aWidget) {
+    this._widget = aWidget;
+
+
+    // Can't use a WeakMap for _itemsByValue because keys are strings, and
+    // can't use one for _itemsByElement either, since it needs to be iterable.
+    XPCOMUtils.defineLazyGetter(this, "_itemsByValue", () => new Map());
+    XPCOMUtils.defineLazyGetter(this, "_itemsByElement", () => new Map());
+    XPCOMUtils.defineLazyGetter(this, "_stagedItems", () => []);
+
+    // Handle internal events emitted by the widget if necessary.
+    if (ViewHelpers.isEventEmitter(aWidget)) {
+      aWidget.on("keyPress", this._onWidgetKeyPress.bind(this));
+      aWidget.on("mousePress", this._onWidgetMousePress.bind(this));
+    }
+  },
+
+  /**
+   * Gets the element node or widget associated with this container.
+   * @return nsIDOMNode | object
+   */
+  get widget() this._widget,
+
+  /**
+   * Prepares an item to be added to this container. This allows, for example,
+   * for a large number of items to be batched up before being sorted & added.
+   *
+   * If the "staged" flag is *not* set to true, the item will be immediately
+   * inserted at the correct position in this container, so that all the items
+   * still remain sorted. This can (possibly) be much slower than batching up
+   * multiple items.
+   *
+   * By default, this container assumes that all the items should be displayed
+   * sorted by their value. This can be overridden with the "index" flag,
+   * specifying on which position should an item be appended. The "staged" and
+   * "index" flags are mutually exclusive, meaning that all staged items
+   * will always be appended.
+   *
+   * @param nsIDOMNode aElement
+   *        A prebuilt node to be wrapped.
+   * @param string aValue
+   *        A string identifying the node.
+   * @param object aOptions [optional]
+   *        Additional options or flags supported by this operation:
+   *          - attachment: some attached primitive/object for the item
+   *          - staged: true to stage the item to be appended later
+   *          - index: specifies on which position should the item be appended
+   *          - attributes: a batch of attributes set to the displayed element
+   *          - finalize: function invoked when the item is removed
+   * @return Item
+   *         The item associated with the displayed element if an unstaged push,
+   *         undefined if the item was staged for a later commit.
+   */
+  push: function([aElement, aValue], aOptions = {}) {
+    let item = new Item(this, aElement, aValue, aOptions.attachment);
+
+    // Batch the item to be added later.
+    if (aOptions.staged) {
+      // An ulterior commit operation will ignore any specified index, so
+      // no reason to keep it around.
+      aOptions.index = undefined;
+      return void this._stagedItems.push({ item: item, options: aOptions });
+    }
+    // Find the target position in this container and insert the item there.
+    if (!("index" in aOptions)) {
+      return this._insertItemAt(this._findExpectedIndexFor(item), item, aOptions);
+    }
+    // Insert the item at the specified index. If negative or out of bounds,
+    // the item will be simply appended.
+    return this._insertItemAt(aOptions.index, item, aOptions);
+  },
+
+  /**
+   * Flushes all the prepared items into this container.
+   * Any specified index on the items will be ignored. Everything is appended.
+   *
+   * @param object aOptions [optional]
+   *        Additional options or flags supported by this operation:
+   *          - sorted: true to sort all the items before adding them
+   */
+  commit: function(aOptions = {}) {
+    let stagedItems = this._stagedItems;
+
+    // Sort the items before adding them to this container, if preferred.
+    if (aOptions.sorted) {
+      stagedItems.sort((a, b) => this._currentSortPredicate(a.item, b.item));
+    }
+    // Append the prepared items to this container.
+    for (let { item, options } of stagedItems) {
+      this._insertItemAt(-1, item, options);
+    }
+    // Recreate the temporary items list for ulterior pushes.
+    this._stagedItems.length = 0;
+  },
+
+  /**
+   * Immediately removes the specified item from this container.
+   *
+   * @param Item aItem
+   *        The item associated with the element to remove.
+   */
+  remove: function(aItem) {
+    if (!aItem) {
+      return;
+    }
+    this._widget.removeChild(aItem._target);
+    this._untangleItem(aItem);
+
+    if (!this._itemsByElement.size) {
+      this._preferredValue = this.selectedValue;
+      this._widget.selectedItem = null;
+      this._widget.setAttribute("emptyText", this._emptyText);
+    }
+  },
+
+  /**
+   * Removes the item at the specified index from this container.
+   *
+   * @param number aIndex
+   *        The index of the item to remove.
+   */
+  removeAt: function(aIndex) {
+    this.remove(this.getItemAtIndex(aIndex));
+  },
+
+  /**
+   * Removes all items from this container.
+   */
+  empty: function() {
+    this._preferredValue = this.selectedValue;
+    this._widget.selectedItem = null;
+    this._widget.removeAllItems();
+    this._widget.setAttribute("emptyText", this._emptyText);
+
+    for (let [, item] of this._itemsByElement) {
+      this._untangleItem(item);
+    }
+
+    this._itemsByValue.clear();
+    this._itemsByElement.clear();
+    this._stagedItems.length = 0;
+  },
+
+  /**
+   * Ensures the specified item is visible in this container.
+   *
+   * @param Item aItem
+   *        The item to bring into view.
+   */
+  ensureItemIsVisible: function(aItem) {
+    this._widget.ensureElementIsVisible(aItem._target);
+  },
+
+  /**
+   * Ensures the item at the specified index is visible in this container.
+   *
+   * @param number aIndex
+   *        The index of the item to bring into view.
+   */
+  ensureIndexIsVisible: function(aIndex) {
+    this.ensureItemIsVisible(this.getItemAtIndex(aIndex));
+  },
+
+  /**
+   * Sugar for ensuring the selected item is visible in this container.
+   */
+  ensureSelectedItemIsVisible: function() {
+    this.ensureItemIsVisible(this.selectedItem);
+  },
+
+  /**
+   * If supported by the widget, the label string temporarily added to this
+   * container when there are no child items present.
+   */
+  set emptyText(aValue) {
+    this._emptyText = aValue;
+
+    // Apply the emptyText attribute right now if there are no child items.
+    if (!this._itemsByElement.size) {
+      this._widget.setAttribute("emptyText", aValue);
+    }
+  },
+
+  /**
+   * If supported by the widget, the label string permanently added to this
+   * container as a header.
+   * @param string aValue
+   */
+  set headerText(aValue) {
+    this._headerText = aValue;
+    this._widget.setAttribute("headerText", aValue);
+  },
+
+  /**
+   * Toggles all the items in this container hidden or visible.
+   *
+   * This does not change the default filtering predicate, so newly inserted
+   * items will always be visible. Use WidgetMethods.filterContents if you care.
+   *
+   * @param boolean aVisibleFlag
+   *        Specifies the intended visibility.
+   */
+  toggleContents: function(aVisibleFlag) {
+    for (let [element, item] of this._itemsByElement) {
+      element.hidden = !aVisibleFlag;
+    }
+  },
+
+  /**
+   * Toggles all items in this container hidden or visible based on a predicate.
+   *
+   * @param function aPredicate [optional]
+   *        Items are toggled according to the return value of this function,
+   *        which will become the new default filtering predicate in this container.
+   *        If unspecified, all items will be toggled visible.
+   */
+  filterContents: function(aPredicate = this._currentFilterPredicate) {
+    this._currentFilterPredicate = aPredicate;
+
+    for (let [element, item] of this._itemsByElement) {
+      element.hidden = !aPredicate(item);
+    }
+  },
+
+  /**
+   * Sorts all the items in this container based on a predicate.
+   *
+   * @param function aPredicate [optional]
+   *        Items are sorted according to the return value of the function,
+   *        which will become the new default sorting predicate in this container.
+   *        If unspecified, all items will be sorted by their value.
+   */
+  sortContents: function(aPredicate = this._currentSortPredicate) {
+    let sortedItems = this.items.sort(this._currentSortPredicate = aPredicate);
+
+    for (let i = 0, len = sortedItems.length; i < len; i++) {
+      this.swapItems(this.getItemAtIndex(i), sortedItems[i]);
+    }
+  },
+
+  /**
+   * Visually swaps two items in this container.
+   *
+   * @param Item aFirst
+   *        The first item to be swapped.
+   * @param Item aSecond
+   *        The second item to be swapped.
+   */
+  swapItems: function(aFirst, aSecond) {
+    if (aFirst == aSecond) { // We're just dandy, thank you.
+      return;
+    }
+    let { _prebuiltNode: firstPrebuiltTarget, _target: firstTarget } = aFirst;
+    let { _prebuiltNode: secondPrebuiltTarget, _target: secondTarget } = aSecond;
+
+    // If the two items were constructed with prebuilt nodes as DocumentFragments,
+    // then those DocumentFragments are now empty and need to be reassembled.
+    if (firstPrebuiltTarget instanceof Ci.nsIDOMDocumentFragment) {
+      for (let node of firstTarget.childNodes) {
+        firstPrebuiltTarget.appendChild(node.cloneNode(true));
+      }
+    }
+    if (secondPrebuiltTarget instanceof Ci.nsIDOMDocumentFragment) {
+      for (let node of secondTarget.childNodes) {
+        secondPrebuiltTarget.appendChild(node.cloneNode(true));
+      }
+    }
+
+    // 1. Get the indices of the two items to swap.
+    let i = this._indexOfElement(firstTarget);
+    let j = this._indexOfElement(secondTarget);
+
+    // 2. Remeber the selection index, to reselect an item, if necessary.
+    let selectedTarget = this._widget.selectedItem;
+    let selectedIndex = -1;
+    if (selectedTarget == firstTarget) {
+      selectedIndex = i;
+    } else if (selectedTarget == secondTarget) {
+      selectedIndex = j;
+    }
+
+    // 3. Silently nuke both items, nobody needs to know about this.
+    this._widget.removeChild(firstTarget);
+    this._widget.removeChild(secondTarget);
+    this._unlinkItem(aFirst);
+    this._unlinkItem(aSecond);
+
+    // 4. Add the items again, but reversing their indices.
+    this._insertItemAt.apply(this, i < j ? [i, aSecond] : [j, aFirst]);
+    this._insertItemAt.apply(this, i < j ? [j, aFirst] : [i, aSecond]);
+
+    // 5. Restore the previous selection, if necessary.
+    if (selectedIndex == i) {
+      this._widget.selectedItem = aFirst._target;
+    } else if (selectedIndex == j) {
+      this._widget.selectedItem = aSecond._target;
+    }
+
+    // 6. Let the outside world know that these two items were swapped.
+    ViewHelpers.dispatchEvent(aFirst.target, "swap", [aSecond, aFirst]);
+  },
+
+  /**
+   * Visually swaps two items in this container at specific indices.
+   *
+   * @param number aFirst
+   *        The index of the first item to be swapped.
+   * @param number aSecond
+   *        The index of the second item to be swapped.
+   */
+  swapItemsAtIndices: function(aFirst, aSecond) {
+    this.swapItems(this.getItemAtIndex(aFirst), this.getItemAtIndex(aSecond));
+  },
+
+  /**
+   * Checks whether an item with the specified value is among the elements
+   * shown in this container.
+   *
+   * @param string aValue
+   *        The item's value.
+   * @return boolean
+   *         True if the value is known, false otherwise.
+   */
+  containsValue: function(aValue) {
+    return this._itemsByValue.has(aValue) ||
+           this._stagedItems.some(({ item }) => item._value == aValue);
+  },
+
+  /**
+   * Gets the "preferred value". This is the latest selected item's value,
+   * remembered just before emptying this container.
+   * @return string
+   */
+  get preferredValue() {
+    return this._preferredValue;
+  },
+
+  /**
+   * Retrieves the item associated with the selected element.
+   * @return Item | null
+   */
+  get selectedItem() {
+    let selectedElement = this._widget.selectedItem;
+    if (selectedElement) {
+      return this._itemsByElement.get(selectedElement);
+    }
+    return null;
+  },
+
+  /**
+   * Retrieves the selected element's index in this container.
+   * @return number
+   */
+  get selectedIndex() {
+    let selectedElement = this._widget.selectedItem;
+    if (selectedElement) {
+      return this._indexOfElement(selectedElement);
+    }
+    return -1;
+  },
+
+  /**
+   * Retrieves the value of the selected element.
+   * @return string
+   */
+  get selectedValue() {
+    let selectedElement = this._widget.selectedItem;
+    if (selectedElement) {
+      return this._itemsByElement.get(selectedElement)._value;
+    }
+    return "";
+  },
+
+  /**
+   * Retrieves the attachment of the selected element.
+   * @return object | null
+   */
+  get selectedAttachment() {
+    let selectedElement = this._widget.selectedItem;
+    if (selectedElement) {
+      return this._itemsByElement.get(selectedElement).attachment;
+    }
+    return null;
+  },
+
+  /**
+   * Selects the element with the entangled item in this container.
+   * @param Item | function aItem
+   */
+  set selectedItem(aItem) {
+    // A predicate is allowed to select a specific item.
+    // If no item is matched, then the current selection is removed.
+    if (typeof aItem == "function") {
+      aItem = this.getItemForPredicate(aItem);
+    }
+
+    // A falsy item is allowed to invalidate the current selection.
+    let targetElement = aItem ? aItem._target : null;
+    let prevElement = this._widget.selectedItem;
+
+    // Make sure the selected item's target element is focused and visible.
+    if (this.autoFocusOnSelection && targetElement) {
+      targetElement.focus();
+    }
+    if (this.maintainSelectionVisible && targetElement) {
+      if ("ensureElementIsVisible" in this._widget) {
+        this._widget.ensureElementIsVisible(targetElement);
+      }
+    }
+
+    // Prevent selecting the same item again and avoid dispatching
+    // a redundant selection event, so return early.
+    if (targetElement != prevElement) {
+      this._widget.selectedItem = targetElement;
+      let dispTarget = targetElement || prevElement;
+      let dispName = this.suppressSelectionEvents ? "suppressed-select" : "select";
+      ViewHelpers.dispatchEvent(dispTarget, dispName, aItem);
+    }
+  },
+
+  /**
+   * Selects the element at the specified index in this container.
+   * @param number aIndex
+   */
+  set selectedIndex(aIndex) {
+    let targetElement = this._widget.getItemAtIndex(aIndex);
+    if (targetElement) {
+      this.selectedItem = this._itemsByElement.get(targetElement);
+      return;
+    }
+    this.selectedItem = null;
+  },
+
+  /**
+   * Selects the element with the specified value in this container.
+   * @param string aValue
+   */
+  set selectedValue(aValue) {
+    this.selectedItem = this._itemsByValue.get(aValue);
+  },
+
+  /**
+   * Specifies if this container should try to keep the selected item visible.
+   * (For example, when new items are added the selection is brought into view).
+   */
+  maintainSelectionVisible: true,
+
+  /**
+   * Specifies if "select" events dispatched from the elements in this container
+   * when their respective items are selected should be suppressed or not.
+   *
+   * If this flag is set to true, then consumers of this container won't
+   * be normally notified when items are selected.
+   */
+  suppressSelectionEvents: false,
+
+  /**
+   * Focus this container the first time an element is inserted?
+   *
+   * If this flag is set to true, then when the first item is inserted in
+   * this container (and thus it's the only item available), its corresponding
+   * target element is focused as well.
+   */
+  autoFocusOnFirstItem: true,
+
+  /**
+   * Focus on selection?
+   *
+   * If this flag is set to true, then whenever an item is selected in
+   * this container (e.g. via the selectedIndex or selectedItem setters),
+   * its corresponding target element is focused as well.
+   *
+   * You can disable this flag, for example, to maintain a certain node
+   * focused but visually indicate a different selection in this container.
+   */
+  autoFocusOnSelection: true,
+
+  /**
+   * Focus on input (e.g. mouse click)?
+   *
+   * If this flag is set to true, then whenever an item receives user input in
+   * this container, its corresponding target element is focused as well.
+   */
+  autoFocusOnInput: true,
+
+  /**
+   * When focusing on input, allow right clicks?
+   * @see WidgetMethods.autoFocusOnInput
+   */
+  allowFocusOnRightClick: false,
+
+  /**
+   * The number of elements in this container to jump when Page Up or Page Down
+   * keys are pressed. If falsy, then the page size will be based on the
+   * number of visible items in the container.
+   */
+  pageSize: 0,
+
+  /**
+   * Focuses the first visible item in this container.
+   */
+  focusFirstVisibleItem: function() {
+    this.focusItemAtDelta(-this.itemCount);
+  },
+
+  /**
+   * Focuses the last visible item in this container.
+   */
+  focusLastVisibleItem: function() {
+    this.focusItemAtDelta(+this.itemCount);
+  },
+
+  /**
+   * Focuses the next item in this container.
+   */
+  focusNextItem: function() {
+    this.focusItemAtDelta(+1);
+  },
+
+  /**
+   * Focuses the previous item in this container.
+   */
+  focusPrevItem: function() {
+    this.focusItemAtDelta(-1);
+  },
+
+  /**
+   * Focuses another item in this container based on the index distance
+   * from the currently focused item.
+   *
+   * @param number aDelta
+   *        A scalar specifying by how many items should the selection change.
+   */
+  focusItemAtDelta: function(aDelta) {
+    // Make sure the currently selected item is also focused, so that the
+    // command dispatcher mechanism has a relative node to work with.
+    // If there's no selection, just select an item at a corresponding index
+    // (e.g. the first item in this container if aDelta <= 1).
+    let selectedElement = this._widget.selectedItem;
+    if (selectedElement) {
+      selectedElement.focus();
+    } else {
+      this.selectedIndex = Math.max(0, aDelta - 1);
+      return;
+    }
+
+    let direction = aDelta > 0 ? "advanceFocus" : "rewindFocus";
+    let distance = Math.abs(Math[aDelta > 0 ? "ceil" : "floor"](aDelta));
+    while (distance--) {
+      if (!this._focusChange(direction)) {
+        break; // Out of bounds.
+      }
+    }
+
+    // Synchronize the selected item as being the currently focused element.
+    this.selectedItem = this.getItemForElement(this._focusedElement);
+  },
+
+  /**
+   * Focuses the next or previous item in this container.
+   *
+   * @param string aDirection
+   *        Either "advanceFocus" or "rewindFocus".
+   * @return boolean
+   *         False if the focus went out of bounds and the first or last item
+   *         in this container was focused instead.
+   */
+  _focusChange: function(aDirection) {
+    let commandDispatcher = this._commandDispatcher;
+    let prevFocusedElement = commandDispatcher.focusedElement;
+    let currFocusedElement;
+
+    do {
+      commandDispatcher.suppressFocusScroll = true;
+      commandDispatcher[aDirection]();
+      currFocusedElement = commandDispatcher.focusedElement;
+
+      // Make sure the newly focused item is a part of this container. If the
+      // focus goes out of bounds, revert the previously focused item.
+      if (!this.getItemForElement(currFocusedElement)) {
+        prevFocusedElement.focus();
+        return false;
+      }
+    } while (!WIDGET_FOCUSABLE_NODES.has(currFocusedElement.tagName));
+
+    // Focus remained within bounds.
+    return true;
+  },
+
+  /**
+   * Gets the command dispatcher instance associated with this container's DOM.
+   * If there are no items displayed in this container, null is returned.
+   * @return nsIDOMXULCommandDispatcher | null
+   */
+  get _commandDispatcher() {
+    if (this._cachedCommandDispatcher) {
+      return this._cachedCommandDispatcher;
+    }
+    let someElement = this._widget.getItemAtIndex(0);
+    if (someElement) {
+      let commandDispatcher = someElement.ownerDocument.commandDispatcher;
+      return this._cachedCommandDispatcher = commandDispatcher;
+    }
+    return null;
+  },
+
+  /**
+   * Gets the currently focused element in this container.
+   *
+   * @return nsIDOMNode
+   *         The focused element, or null if nothing is found.
+   */
+  get _focusedElement() {
+    let commandDispatcher = this._commandDispatcher;
+    if (commandDispatcher) {
+      return commandDispatcher.focusedElement;
+    }
+    return null;
+  },
+
+  /**
+   * Gets the item in the container having the specified index.
+   *
+   * @param number aIndex
+   *        The index used to identify the element.
+   * @return Item
+   *         The matched item, or null if nothing is found.
+   */
+  getItemAtIndex: function(aIndex) {
+    return this.getItemForElement(this._widget.getItemAtIndex(aIndex));
+  },
+
+  /**
+   * Gets the item in the container having the specified value.
+   *
+   * @param string aValue
+   *        The value used to identify the element.
+   * @return Item
+   *         The matched item, or null if nothing is found.
+   */
+  getItemByValue: function(aValue) {
+    return this._itemsByValue.get(aValue);
+  },
+
+  /**
+   * Gets the item in the container associated with the specified element.
+   *
+   * @param nsIDOMNode aElement
+   *        The element used to identify the item.
+   * @param object aFlags [optional]
+   *        Additional options for showing the source. Supported options:
+   *          - noSiblings: if siblings shouldn't be taken into consideration
+   *                        when searching for the associated item.
+   * @return Item
+   *         The matched item, or null if nothing is found.
+   */
+  getItemForElement: function(aElement, aFlags = {}) {
+    while (aElement) {
+      let item = this._itemsByElement.get(aElement);
+
+      // Also search the siblings if allowed.
+      if (!aFlags.noSiblings) {
+        item = item ||
+          this._itemsByElement.get(aElement.nextElementSibling) ||
+          this._itemsByElement.get(aElement.previousElementSibling);
+      }
+      if (item) {
+        return item;
+      }
+      aElement = aElement.parentNode;
+    }
+    return null;
+  },
+
+  /**
+   * Gets a visible item in this container validating a specified predicate.
+   *
+   * @param function aPredicate
+   *        The first item which validates this predicate is returned
+   * @return Item
+   *         The matched item, or null if nothing is found.
+   */
+  getItemForPredicate: function(aPredicate, aOwner = this) {
+    // Recursively check the items in this widget for a predicate match.
+    for (let [element, item] of aOwner._itemsByElement) {
+      let match;
+      if (aPredicate(item) && !element.hidden) {
+        match = item;
+      } else {
+        match = this.getItemForPredicate(aPredicate, item);
+      }
+      if (match) {
+        return match;
+      }
+    }
+    // Also check the staged items. No need to do this recursively since
+    // they're not even appended to the view yet.
+    for (let { item } of this._stagedItems) {
+      if (aPredicate(item)) {
+        return item;
+      }
+    }
+    return null;
+  },
+
+  /**
+   * Shortcut function for getItemForPredicate which works on item attachments.
+   * @see getItemForPredicate
+   */
+  getItemForAttachment: function(aPredicate, aOwner = this) {
+    return this.getItemForPredicate(e => aPredicate(e.attachment));
+  },
+
+  /**
+   * Finds the index of an item in the container.
+   *
+   * @param Item aItem
+   *        The item get the index for.
+   * @return number
+   *         The index of the matched item, or -1 if nothing is found.
+   */
+  indexOfItem: function(aItem) {
+    return this._indexOfElement(aItem._target);
+  },
+
+  /**
+   * Finds the index of an element in the container.
+   *
+   * @param nsIDOMNode aElement
+   *        The element get the index for.
+   * @return number
+   *         The index of the matched element, or -1 if nothing is found.
+   */
+  _indexOfElement: function(aElement) {
+    for (let i = 0; i < this._itemsByElement.size; i++) {
+      if (this._widget.getItemAtIndex(i) == aElement) {
+        return i;
+      }
+    }
+    return -1;
+  },
+
+  /**
+   * Gets the total number of items in this container.
+   * @return number
+   */
+  get itemCount() {
+    return this._itemsByElement.size;
+  },
+
+  /**
+   * Returns a list of items in this container, in the displayed order.
+   * @return array
+   */
+  get items() {
+    let store = [];
+    let itemCount = this.itemCount;
+    for (let i = 0; i < itemCount; i++) {
+      store.push(this.getItemAtIndex(i));
+    }
+    return store;
+  },
+
+  /**
+   * Returns a list of values in this container, in the displayed order.
+   * @return array
+   */
+  get values() {
+    return this.items.map(e => e._value);
+  },
+
+  /**
+   * Returns a list of attachments in this container, in the displayed order.
+   * @return array
+   */
+  get attachments() {
+    return this.items.map(e => e.attachment);
+  },
+
+  /**
+   * Returns a list of all the visible (non-hidden) items in this container,
+   * in the displayed order
+   * @return array
+   */
+  get visibleItems() {
+    return this.items.filter(e => !e._target.hidden);
+  },
+
+  /**
+   * Checks if an item is unique in this container. If an item's value is an
+   * empty string, "undefined" or "null", it is considered unique.
+   *
+   * @param Item aItem
+   *        The item for which to verify uniqueness.
+   * @return boolean
+   *         True if the item is unique, false otherwise.
+   */
+  isUnique: function(aItem) {
+    let value = aItem._value;
+    if (value == "" || value == "undefined" || value == "null") {
+      return true;
+    }
+    return !this._itemsByValue.has(value);
+  },
+
+  /**
+   * Checks if an item is eligible for this container. By default, this checks
+   * whether an item is unique and has a prebuilt target node.
+   *
+   * @param Item aItem
+   *        The item for which to verify eligibility.
+   * @return boolean
+   *         True if the item is eligible, false otherwise.
+   */
+  isEligible: function(aItem) {
+    return this.isUnique(aItem) && aItem._prebuiltNode;
+  },
+
+  /**
+   * Finds the expected item index in this container based on the default
+   * sort predicate.
+   *
+   * @param Item aItem
+   *        The item for which to get the expected index.
+   * @return number
+   *         The expected item index.
+   */
+  _findExpectedIndexFor: function(aItem) {
+    let itemCount = this.itemCount;
+    for (let i = 0; i < itemCount; i++) {
+      if (this._currentSortPredicate(this.getItemAtIndex(i), aItem) > 0) {
+        return i;
+      }
+    }
+    return itemCount;
+  },
+
+  /**
+   * Immediately inserts an item in this container at the specified index.
+   *
+   * @param number aIndex
+   *        The position in the container intended for this item.
+   * @param Item aItem
+   *        The item describing a target element.
+   * @param object aOptions [optional]
+   *        Additional options or flags supported by this operation:
+   *          - attributes: a batch of attributes set to the displayed element
+   *          - finalize: function when the item is untangled (removed)
+   * @return Item
+   *         The item associated with the displayed element, null if rejected.
+   */
+  _insertItemAt: function(aIndex, aItem, aOptions = {}) {
+    if (!this.isEligible(aItem)) {
+      return null;
+    }
+
+    // Entangle the item with the newly inserted node.
+    // Make sure this is done with the value returned by insertItemAt(),
+    // to avoid storing a potential DocumentFragment.
+    let node = aItem._prebuiltNode;
+    let attachment = aItem.attachment;
+    this._entangleItem(aItem, this._widget.insertItemAt(aIndex, node, attachment));
+
+    // Handle any additional options after entangling the item.
+    if (!this._currentFilterPredicate(aItem)) {
+      aItem._target.hidden = true;
+    }
+    if (this.autoFocusOnFirstItem && this._itemsByElement.size == 1) {
+      aItem._target.focus();
+    }
+    if (aOptions.attributes) {
+      aOptions.attributes.forEach(e => aItem._target.setAttribute(e[0], e[1]));
+    }
+    if (aOptions.finalize) {
+      aItem.finalize = aOptions.finalize;
+    }
+
+    // Hide the empty text if the selection wasn't lost.
+    this._widget.removeAttribute("emptyText");
+
+    // Return the item associated with the displayed element.
+    return aItem;
+  },
+
+  /**
+   * Entangles an item (model) with a displayed node element (view).
+   *
+   * @param Item aItem
+   *        The item describing a target element.
+   * @param nsIDOMNode aElement
+   *        The element displaying the item.
+   */
+  _entangleItem: function(aItem, aElement) {
+    this._itemsByValue.set(aItem._value, aItem);
+    this._itemsByElement.set(aElement, aItem);
+    aItem._target = aElement;
+  },
+
+  /**
+   * Untangles an item (model) from a displayed node element (view).
+   *
+   * @param Item aItem
+   *        The item describing a target element.
+   */
+  _untangleItem: function(aItem) {
+    if (aItem.finalize) {
+      aItem.finalize(aItem);
+    }
+    for (let childItem of aItem) {
+      aItem.remove(childItem);
+    }
+
+    this._unlinkItem(aItem);
+    aItem._target = null;
+  },
+
+  /**
+   * Deletes an item from the its parent's storage maps.
+   *
+   * @param Item aItem
+   *        The item describing a target element.
+   */
+  _unlinkItem: function(aItem) {
+    this._itemsByValue.delete(aItem._value);
+    this._itemsByElement.delete(aItem._target);
+  },
+
+  /**
+   * The keyPress event listener for this container.
+   * @param string aName
+   * @param KeyboardEvent aEvent
+   */
+  _onWidgetKeyPress: function(aName, aEvent) {
+    // Prevent scrolling when pressing navigation keys.
+    ViewHelpers.preventScrolling(aEvent);
+
+    switch (aEvent.keyCode) {
+      case aEvent.DOM_VK_UP:
+      case aEvent.DOM_VK_LEFT:
+        this.focusPrevItem();
+        return;
+      case aEvent.DOM_VK_DOWN:
+      case aEvent.DOM_VK_RIGHT:
+        this.focusNextItem();
+        return;
+      case aEvent.DOM_VK_PAGE_UP:
+        this.focusItemAtDelta(-(this.pageSize || (this.itemCount / PAGE_SIZE_ITEM_COUNT_RATIO)));
+        return;
+      case aEvent.DOM_VK_PAGE_DOWN:
+        this.focusItemAtDelta(+(this.pageSize || (this.itemCount / PAGE_SIZE_ITEM_COUNT_RATIO)));
+        return;
+      case aEvent.DOM_VK_HOME:
+        this.focusFirstVisibleItem();
+        return;
+      case aEvent.DOM_VK_END:
+        this.focusLastVisibleItem();
+        return;
+    }
+  },
+
+  /**
+   * The mousePress event listener for this container.
+   * @param string aName
+   * @param MouseEvent aEvent
+   */
+  _onWidgetMousePress: function(aName, aEvent) {
+    if (aEvent.button != 0 && !this.allowFocusOnRightClick) {
+      // Only allow left-click to trigger this event.
+      return;
+    }
+
+    let item = this.getItemForElement(aEvent.target);
+    if (item) {
+      // The container is not empty and we clicked on an actual item.
+      this.selectedItem = item;
+      // Make sure the current event's target element is also focused.
+      this.autoFocusOnInput && item._target.focus();
+    }
+  },
+
+  /**
+   * The predicate used when filtering items. By default, all items in this
+   * view are visible.
+   *
+   * @param Item aItem
+   *        The item passing through the filter.
+   * @return boolean
+   *         True if the item should be visible, false otherwise.
+   */
+  _currentFilterPredicate: function(aItem) {
+    return true;
+  },
+
+  /**
+   * The predicate used when sorting items. By default, items in this view
+   * are sorted by their label.
+   *
+   * @param Item aFirst
+   *        The first item used in the comparison.
+   * @param Item aSecond
+   *        The second item used in the comparison.
+   * @return number
+   *         -1 to sort aFirst to a lower index than aSecond
+   *          0 to leave aFirst and aSecond unchanged with respect to each other
+   *          1 to sort aSecond to a lower index than aFirst
+   */
+  _currentSortPredicate: function(aFirst, aSecond) {
+    return +(aFirst._value.toLowerCase() > aSecond._value.toLowerCase());
+  },
+
+  /**
+   * Call a method on this widget named `aMethodName`. Any further arguments are
+   * passed on to the method. Returns the result of the method call.
+   *
+   * @param String aMethodName
+   *        The name of the method you want to call.
+   * @param aArgs
+   *        Optional. Any arguments you want to pass through to the method.
+   */
+  callMethod: function(aMethodName, ...aArgs) {
+    return this._widget[aMethodName].apply(this._widget, aArgs);
+  },
+
+  _widget: null,
+  _emptyText: "",
+  _headerText: "",
+  _preferredValue: "",
+  _cachedCommandDispatcher: null
+};
+
+/**
+ * A generator-iterator over all the items in this container.
+ */
+Item.prototype["@@iterator"] =
+WidgetMethods["@@iterator"] = function*() {
+  yield* this._itemsByElement.values();
+};