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ui/accessibility/extensions/caretbrowsing/caretbrowsing.js

-/* Copyright (c) 2014 The Chromium Authors. All rights reserved.
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file. */
-
-/**
- * @fileoverview Caret browsing content script, runs in each frame.
- *
- * The behavior is based on Mozilla's spec whenever possible:
- *   http://www.mozilla.org/access/keyboard/proposal
- *
- * The one exception is that Esc is used to escape out of a form control,
- * rather than their proposed key (which doesn't seem to work in the
- * latest Firefox anyway).
- *
- * Some details about how Chrome selection works, which will help in
- * understanding the code:
- *
- * The Selection object (window.getSelection()) has four components that
- * completely describe the state of the caret or selection:
- *
- * base and anchor: this is the start of the selection, the fixed point.
- * extent and focus: this is the end of the selection, the part that
- *     moves when you hold down shift and press the left or right arrows.
- *
- * When the selection is a cursor, the base, anchor, extent, and focus are
- * all the same.
- *
- * There's only one time when the base and anchor are not the same, or the
- * extent and focus are not the same, and that's when the selection is in
- * an ambiguous state - i.e. it's not clear which edge is the focus and which
- * is the anchor. As an example, if you double-click to select a word, then
- * the behavior is dependent on your next action. If you press Shift+Right,
- * the right edge becomes the focus. But if you press Shift+Left, the left
- * edge becomes the focus.
- *
- * When the selection is in an ambiguous state, the base and extent are set
- * to the position where the mouse clicked, and the anchor and focus are set
- * to the boundaries of the selection.
- *
- * The only way to set the selection and give it direction is to use
- * the non-standard Selection.setBaseAndExtent method. If you try to use
- * Selection.addRange(), the anchor will always be on the left and the focus
- * will always be on the right, making it impossible to manipulate
- * selections that move from right to left.
- *
- * Finally, Chrome will throw an exception if you try to set an invalid
- * selection - a selection where the left and right edges are not the same,
- * but it doesn't span any visible characters. A common example is that
- * there are often many whitespace characters in the DOM that are not
- * visible on the page; trying to select them will fail. Another example is
- * any node that's invisible or not displayed.
- *
- * While there are probably many possible methods to determine what is
- * selectable, this code uses the method of determining if there's a valid
- * bounding box for the range or not - keep moving the cursor forwards until
- * the range from the previous position and candidate next position has a
- * valid bounding box.
- */
-
-/**
- * Return whether a node is focusable. This includes nodes whose tabindex
- * attribute is set to "-1" explicitly - these nodes are not in the tab
- * order, but they should still be focused if the user navigates to them
- * using linear or smart DOM navigation.
- *
- * Note that when the tabIndex property of an Element is -1, that doesn't
- * tell us whether the tabIndex attribute is missing or set to "-1" explicitly,
- * so we have to check the attribute.
- *
- * @param {Object} targetNode The node to check if it's focusable.
- * @return {boolean} True if the node is focusable.
- */
-function isFocusable(targetNode) {
-  if (!targetNode || typeof(targetNode.tabIndex) != 'number') {
-    return false;
-  }
-
-  if (targetNode.tabIndex >= 0) {
-    return true;
-  }
-
-  if (targetNode.hasAttribute &&
-      targetNode.hasAttribute('tabindex') &&
-      targetNode.getAttribute('tabindex') == '-1') {
-    return true;
-  }
-
-  return false;
-}
-
-/**
- * Determines whether or not a node is or is the descendant of another node.
- *
- * @param {Object} node The node to be checked.
- * @param {Object} ancestor The node to see if it's a descendant of.
- * @return {boolean} True if the node is ancestor or is a descendant of it.
- */
-function isDescendantOfNode(node, ancestor) {
-  while (node && ancestor) {
-    if (node.isSameNode(ancestor)) {
-      return true;
-    }
-    node = node.parentNode;
-  }
-  return false;
-}
-
-
-
-/**
- * The class handling the Caret Browsing implementation in the page.
- * Installs a keydown listener that always responds to the F7 key,
- * sets up communication with the background page, and then when caret
- * browsing is enabled, response to various key events to move the caret
- * or selection within the text content of the document. Uses the native
- * Chrome selection wherever possible, but displays its own flashing
- * caret using a DIV because there's no native caret available.
- * @constructor
- */
-var CaretBrowsing = function() {};
-
-/**
- * Is caret browsing enabled?
- * @type {boolean}
- */
-CaretBrowsing.isEnabled = false;
-
-/**
- * Keep it enabled even when flipped off (for the options page)?
- * @type {boolean}
- */
-CaretBrowsing.forceEnabled = false;
-
-/**
- * What to do when the caret appears?
- * @type {string}
- */
-CaretBrowsing.onEnable;
-
-/**
- * What to do when the caret jumps?
- * @type {string}
- */
-CaretBrowsing.onJump;
-
-/**
- * Is this window / iframe focused? We won't show the caret if not,
- * especially so that carets aren't shown in two iframes of the same
- * tab.
- * @type {boolean}
- */
-CaretBrowsing.isWindowFocused = false;
-
-/**
- * Is the caret actually visible? This is true only if isEnabled and
- * isWindowFocused are both true.
- * @type {boolean}
- */
-CaretBrowsing.isCaretVisible = false;
-
-/**
- * The actual caret element, an absolute-positioned flashing line.
- * @type {Element}
- */
-CaretBrowsing.caretElement;
-
-/**
- * The x-position of the caret, in absolute pixels.
- * @type {number}
- */
-CaretBrowsing.caretX = 0;
-
-/**
- * The y-position of the caret, in absolute pixels.
- * @type {number}
- */
-CaretBrowsing.caretY = 0;
-
-/**
- * The width of the caret in pixels.
- * @type {number}
- */
-CaretBrowsing.caretWidth = 0;
-
-/**
- * The height of the caret in pixels.
- * @type {number}
- */
-CaretBrowsing.caretHeight = 0;
-
-/**
- * The foregroundc color.
- * @type {string}
- */
-CaretBrowsing.caretForeground = '#000';
-
-/**
- * The backgroundc color.
- * @type {string}
- */
-CaretBrowsing.caretBackground = '#fff';
-
-/**
- * Is the selection collapsed, i.e. are the start and end locations
- * the same? If so, our blinking caret image is shown; otherwise
- * the Chrome selection is shown.
- * @type {boolean}
- */
-CaretBrowsing.isSelectionCollapsed = false;
-
-/**
- * The id returned by window.setInterval for our blink function, so
- * we can cancel it when caret browsing is disabled.
- * @type {number?}
- */
-CaretBrowsing.blinkFunctionId = null;
-
-/**
- * The desired x-coordinate to match when moving the caret up and down.
- * To match the behavior as documented in Mozilla's caret browsing spec
- * (http://www.mozilla.org/access/keyboard/proposal), we keep track of the
- * initial x position when the user starts moving the caret up and down,
- * so that the x position doesn't drift as you move throughout lines, but
- * stays as close as possible to the initial position. This is reset when
- * moving left or right or clicking.
- * @type {number?}
- */
-CaretBrowsing.targetX = null;
-
-/**
- * A flag that flips on or off as the caret blinks.
- * @type {boolean}
- */
-CaretBrowsing.blinkFlag = true;
-
-/**
- * Whether or not we're on a Mac - affects modifier keys.
- * @type {boolean}
- */
-CaretBrowsing.isMac = (navigator.appVersion.indexOf("Mac") != -1);
-
-/**
- * Check if a node is a control that normally allows the user to interact
- * with it using arrow keys. We won't override the arrow keys when such a
- * control has focus, the user must press Escape to do caret browsing outside
- * that control.
- * @param {Node} node A node to check.
- * @return {boolean} True if this node is a control that the user can
- *     interact with using arrow keys.
- */
-CaretBrowsing.isControlThatNeedsArrowKeys = function(node) {
-  if (!node) {
-    return false;
-  }
-
-  if (node == document.body || node != document.activeElement) {
-    return false;
-  }
-
-  if (node.constructor == HTMLSelectElement) {
-    return true;
-  }
-
-  if (node.constructor == HTMLInputElement) {
-    switch (node.type) {
-      case 'email':
-      case 'number':
-      case 'password':
-      case 'search':
-      case 'text':
-      case 'tel':
-      case 'url':
-      case '':
-        return true;  // All of these are text boxes.
-      case 'datetime':
-      case 'datetime-local':
-      case 'date':
-      case 'month':
-      case 'radio':
-      case 'range':
-      case 'week':
-        return true;  // These are other input elements that use arrows.
-    }
-  }
-
-  // Handle focusable ARIA controls.
-  if (node.getAttribute && isFocusable(node)) {
-    var role = node.getAttribute('role');
-    switch (role) {
-      case 'combobox':
-      case 'grid':
-      case 'gridcell':
-      case 'listbox':
-      case 'menu':
-      case 'menubar':
-      case 'menuitem':
-      case 'menuitemcheckbox':
-      case 'menuitemradio':
-      case 'option':
-      case 'radiogroup':
-      case 'scrollbar':
-      case 'slider':
-      case 'spinbutton':
-      case 'tab':
-      case 'tablist':
-      case 'textbox':
-      case 'tree':
-      case 'treegrid':
-      case 'treeitem':
-        return true;
-    }
-  }
-
-  return false;
-};
-
-/**
- * If there's no initial selection, set the cursor just before the
- * first text character in the document.
- */
-CaretBrowsing.setInitialCursor = function() {
-  var sel = window.getSelection();
-  if (sel.rangeCount > 0) {
-    return;
-  }
-
-  var start = new Cursor(document.body, 0, '');
-  var end = new Cursor(document.body, 0, '');
-  var nodesCrossed = [];
-  var result = TraverseUtil.getNextChar(start, end, nodesCrossed, true);
-  if (result == null) {
-    return;
-  }
-  CaretBrowsing.setAndValidateSelection(start, start);
-};
-
-/**
- * Set focus to a node if it's focusable. If it's an input element,
- * select the text, otherwise it doesn't appear focused to the user.
- * Every other control behaves normally if you just call focus() on it.
- * @param {Node} node The node to focus.
- * @return {boolean} True if the node was focused.
- */
-CaretBrowsing.setFocusToNode = function(node) {
-  while (node && node != document.body) {
-    if (isFocusable(node) && node.constructor != HTMLIFrameElement) {
-      node.focus();
-      if (node.constructor == HTMLInputElement && node.select) {
-        node.select();
-      }
-      return true;
-    }
-    node = node.parentNode;
-  }
-
-  return false;
-};
-
-/**
- * Set focus to the first focusable node in the given list.
- * select the text, otherwise it doesn't appear focused to the user.
- * Every other control behaves normally if you just call focus() on it.
- * @param {Array.<Node>} nodeList An array of nodes to focus.
- * @return {boolean} True if the node was focused.
- */
-CaretBrowsing.setFocusToFirstFocusable = function(nodeList) {
-  for (var i = 0; i < nodeList.length; i++) {
-    if (CaretBrowsing.setFocusToNode(nodeList[i])) {
-      return true;
-    }
-  }
-  return false;
-};
-
-/**
- * Set the caret element's normal style, i.e. not when animating.
- */
-CaretBrowsing.setCaretElementNormalStyle = function() {
-  var element = CaretBrowsing.caretElement;
-  element.className = 'CaretBrowsing_Caret';
-  element.style.opacity = CaretBrowsing.isSelectionCollapsed ? '1.0' : '0.0';
-  element.style.left = CaretBrowsing.caretX + 'px';
-  element.style.top = CaretBrowsing.caretY + 'px';
-  element.style.width = CaretBrowsing.caretWidth + 'px';
-  element.style.height = CaretBrowsing.caretHeight + 'px';
-  element.style.color = CaretBrowsing.caretForeground;
-};
-
-/**
- * Animate the caret element into the normal style.
- */
-CaretBrowsing.animateCaretElement = function() {
-  var element = CaretBrowsing.caretElement;
-  element.style.left = (CaretBrowsing.caretX - 50) + 'px';
-  element.style.top = (CaretBrowsing.caretY - 100) + 'px';
-  element.style.width = (CaretBrowsing.caretWidth + 100) + 'px';
-  element.style.height = (CaretBrowsing.caretHeight + 200) + 'px';
-  element.className = 'CaretBrowsing_AnimateCaret';
-
-  // Start the animation. The setTimeout is so that the old values will get
-  // applied first, so we can animate to the new values.
-  window.setTimeout(function() {
-    if (!CaretBrowsing.caretElement) {
-      return;
-    }
-    CaretBrowsing.setCaretElementNormalStyle();
-    element.style['-webkit-transition'] = 'all 0.8s ease-in';
-    function listener() {
-      element.removeEventListener(
-          'webkitTransitionEnd', listener, false);
-      element.style['-webkit-transition'] = 'none';
-    }
-    element.addEventListener(
-        'webkitTransitionEnd', listener, false);
-  }, 0);
-};
-
-/**
- * Quick flash and then show the normal caret style.
- */
-CaretBrowsing.flashCaretElement = function() {
-  var x = CaretBrowsing.caretX - window.pageXOffset;
-  var y = CaretBrowsing.caretY - window.pageYOffset;
-  var height = CaretBrowsing.caretHeight;
-
-  var vert = document.createElement('div');
-  vert.className = 'CaretBrowsing_FlashVert';
-  vert.style.left = (x - 6) + 'px';
-  vert.style.top = (y - 100) + 'px';
-  vert.style.width = '11px';
-  vert.style.height = (200) + 'px';
-  document.body.appendChild(vert);
-
-  window.setTimeout(function() {
-    document.body.removeChild(vert);
-    if (CaretBrowsing.caretElement) {
-      CaretBrowsing.setCaretElementNormalStyle();
-    }
-  }, 250);
-};
-
-/**
- * Create the caret element. This assumes that caretX, caretY,
- * caretWidth, and caretHeight have all been set. The caret is
- * animated in so the user can find it when it first appears.
- */
-CaretBrowsing.createCaretElement = function() {
-  var element = document.createElement('div');
-  element.className = 'CaretBrowsing_Caret';
-  document.body.appendChild(element);
-  CaretBrowsing.caretElement = element;
-
-  if (CaretBrowsing.onEnable == 'anim') {
-    CaretBrowsing.animateCaretElement();
-  } else if (CaretBrowsing.onEnable == 'flash') {
-    CaretBrowsing.flashCaretElement();
-  } else {
-    CaretBrowsing.setCaretElementNormalStyle();
-  }
-};
-
-/**
- * Recreate the caret element, triggering any intro animation.
- */
-CaretBrowsing.recreateCaretElement = function() {
-  if (CaretBrowsing.caretElement) {
-    window.clearInterval(CaretBrowsing.blinkFunctionId);
-    CaretBrowsing.caretElement.parentElement.removeChild(
-        CaretBrowsing.caretElement);
-    CaretBrowsing.caretElement = null;
-    CaretBrowsing.updateIsCaretVisible();
-  }
-};
-
-/**
- * Get the rectangle for a cursor position. This is tricky because
- * you can't get the bounding rectangle of an empty range, so this function
- * computes the rect by trying a range including one character earlier or
- * later than the cursor position.
- * @param {Cursor} cursor A single cursor position.
- * @return {{left: number, top: number, width: number, height: number}}
- *     The bounding rectangle of the cursor.
- */
-CaretBrowsing.getCursorRect = function(cursor) {
-  var node = cursor.node;
-  var index = cursor.index;
-  var rect = {
-    left: 0,
-    top: 0,
-    width: 1,
-    height: 0
-  };
-  if (node.constructor == Text) {
-    var left = index;
-    var right = index;
-    var max = node.data.length;
-    var newRange = document.createRange();
-    while (left > 0 || right < max) {
-      if (left > 0) {
-        left--;
-        newRange.setStart(node, left);
-        newRange.setEnd(node, index);
-        var rangeRect = newRange.getBoundingClientRect();
-        if (rangeRect && rangeRect.width && rangeRect.height) {
-          rect.left = rangeRect.right;
-          rect.top = rangeRect.top;
-          rect.height = rangeRect.height;
-          break;
-        }
-      }
-      if (right < max) {
-        right++;
-        newRange.setStart(node, index);
-        newRange.setEnd(node, right);
-        var rangeRect = newRange.getBoundingClientRect();
-        if (rangeRect && rangeRect.width && rangeRect.height) {
-          rect.left = rangeRect.left;
-          rect.top = rangeRect.top;
-          rect.height = rangeRect.height;
-          break;
-        }
-      }
-    }
-  } else {
-    rect.height = node.offsetHeight;
-    while (node !== null) {
-      rect.left += node.offsetLeft;
-      rect.top += node.offsetTop;
-      node = node.offsetParent;
-    }
-  }
-  rect.left += window.pageXOffset;
-  rect.top += window.pageYOffset;
-  return rect;
-};
-
-/**
- * Compute the new location of the caret or selection and update
- * the element as needed.
- * @param {boolean} scrollToSelection If true, will also scroll the page
- *     to the caret / selection location.
- */
-CaretBrowsing.updateCaretOrSelection = function(scrollToSelection) {
-  var previousX = CaretBrowsing.caretX;
-  var previousY = CaretBrowsing.caretY;
-
-  var sel = window.getSelection();
-  if (sel.rangeCount == 0) {
-    if (CaretBrowsing.caretElement) {
-      CaretBrowsing.isSelectionCollapsed = false;
-      CaretBrowsing.caretElement.style.opacity = '0.0';
-    }
-    return;
-  }
-
-  var range = sel.getRangeAt(0);
-  if (!range) {
-    if (CaretBrowsing.caretElement) {
-      CaretBrowsing.isSelectionCollapsed = false;
-      CaretBrowsing.caretElement.style.opacity = '0.0';
-    }
-    return;
-  }
-
-  if (CaretBrowsing.isControlThatNeedsArrowKeys(document.activeElement)) {
-    var node = document.activeElement;
-    CaretBrowsing.caretWidth = node.offsetWidth;
-    CaretBrowsing.caretHeight = node.offsetHeight;
-    CaretBrowsing.caretX = 0;
-    CaretBrowsing.caretY = 0;
-    while (node.offsetParent) {
-      CaretBrowsing.caretX += node.offsetLeft;
-      CaretBrowsing.caretY += node.offsetTop;
-      node = node.offsetParent;
-    }
-    CaretBrowsing.isSelectionCollapsed = false;
-  } else if (range.startOffset != range.endOffset ||
-             range.startContainer != range.endContainer) {
-    var rect = range.getBoundingClientRect();
-    if (!rect) {
-      return;
-    }
-    CaretBrowsing.caretX = rect.left + window.pageXOffset;
-    CaretBrowsing.caretY = rect.top + window.pageYOffset;
-    CaretBrowsing.caretWidth = rect.width;
-    CaretBrowsing.caretHeight = rect.height;
-    CaretBrowsing.isSelectionCollapsed = false;
-  } else {
-    var rect = CaretBrowsing.getCursorRect(
-        new Cursor(range.startContainer,
-                   range.startOffset,
-                   TraverseUtil.getNodeText(range.startContainer)));
-    CaretBrowsing.caretX = rect.left;
-    CaretBrowsing.caretY = rect.top;
-    CaretBrowsing.caretWidth = rect.width;
-    CaretBrowsing.caretHeight = rect.height;
-    CaretBrowsing.isSelectionCollapsed = true;
-  }
-
-  if (!CaretBrowsing.caretElement) {
-    CaretBrowsing.createCaretElement();
-  } else {
-    var element = CaretBrowsing.caretElement;
-    if (CaretBrowsing.isSelectionCollapsed) {
-      element.style.opacity = '1.0';
-      element.style.left = CaretBrowsing.caretX + 'px';
-      element.style.top = CaretBrowsing.caretY + 'px';
-      element.style.width = CaretBrowsing.caretWidth + 'px';
-      element.style.height = CaretBrowsing.caretHeight + 'px';
-    } else {
-      element.style.opacity = '0.0';
-    }
-  }
-
-  var elem = range.startContainer;
-  if (elem.constructor == Text)
-    elem = elem.parentElement;
-  var style = window.getComputedStyle(elem);
-  var bg = axs.utils.getBgColor(style, elem);
-  var fg = axs.utils.getFgColor(style, elem, bg);
-  CaretBrowsing.caretBackground = axs.utils.colorToString(bg);
-  CaretBrowsing.caretForeground = axs.utils.colorToString(fg);
-
-  if (scrollToSelection) {
-    // Scroll just to the "focus" position of the selection,
-    // the part the user is manipulating.
-    var rect = CaretBrowsing.getCursorRect(
-        new Cursor(sel.focusNode, sel.focusOffset,
-                   TraverseUtil.getNodeText(sel.focusNode)));
-
-    var yscroll = window.pageYOffset;
-    var pageHeight = window.innerHeight;
-    var caretY = rect.top;
-    var caretHeight = Math.min(rect.height, 30);
-    if (yscroll + pageHeight < caretY + caretHeight) {
-      window.scroll(0, (caretY + caretHeight - pageHeight + 100));
-    } else if (caretY < yscroll) {
-      window.scroll(0, (caretY - 100));
-    }
-  }
-
-  if (Math.abs(previousX - CaretBrowsing.caretX) > 500 ||
-      Math.abs(previousY - CaretBrowsing.caretY) > 100) {
-    if (CaretBrowsing.onJump == 'anim') {
-      CaretBrowsing.animateCaretElement();
-    } else if (CaretBrowsing.onJump == 'flash') {
-      CaretBrowsing.flashCaretElement();
-    }
-  }
-};
-
-/**
- * Return true if the selection directionality is ambiguous, which happens
- * if, for example, the user double-clicks in the middle of a word to select
- * it. In that case, the selection should extend by the right edge if the
- * user presses right, and by the left edge if the user presses left.
- * @param {Selection} sel The selection.
- * @return {boolean} True if the selection directionality is ambiguous.
- */
-CaretBrowsing.isAmbiguous = function(sel) {
-  return (sel.anchorNode != sel.baseNode ||
-          sel.anchorOffset != sel.baseOffset ||
-          sel.focusNode != sel.extentNode ||
-          sel.focusOffset != sel.extentOffset);
-};
-
-/**
- * Create a Cursor from the anchor position of the selection, the
- * part that doesn't normally move.
- * @param {Selection} sel The selection.
- * @return {Cursor} A cursor pointing to the selection's anchor location.
- */
-CaretBrowsing.makeAnchorCursor = function(sel) {
-  return new Cursor(sel.anchorNode, sel.anchorOffset,
-                    TraverseUtil.getNodeText(sel.anchorNode));
-};
-
-/**
- * Create a Cursor from the focus position of the selection.
- * @param {Selection} sel The selection.
- * @return {Cursor} A cursor pointing to the selection's focus location.
- */
-CaretBrowsing.makeFocusCursor = function(sel) {
-  return new Cursor(sel.focusNode, sel.focusOffset,
-                    TraverseUtil.getNodeText(sel.focusNode));
-};
-
-/**
- * Create a Cursor from the left boundary of the selection - the boundary
- * closer to the start of the document.
- * @param {Selection} sel The selection.
- * @return {Cursor} A cursor pointing to the selection's left boundary.
- */
-CaretBrowsing.makeLeftCursor = function(sel) {
-  var range = sel.rangeCount == 1 ? sel.getRangeAt(0) : null;
-  if (range &&
-      range.endContainer == sel.anchorNode &&
-      range.endOffset == sel.anchorOffset) {
-    return CaretBrowsing.makeFocusCursor(sel);
-  } else {
-    return CaretBrowsing.makeAnchorCursor(sel);
-  }
-};
-
-/**
- * Create a Cursor from the right boundary of the selection - the boundary
- * closer to the end of the document.
- * @param {Selection} sel The selection.
- * @return {Cursor} A cursor pointing to the selection's right boundary.
- */
-CaretBrowsing.makeRightCursor = function(sel) {
-  var range = sel.rangeCount == 1 ? sel.getRangeAt(0) : null;
-  if (range &&
-      range.endContainer == sel.anchorNode &&
-      range.endOffset == sel.anchorOffset) {
-    return CaretBrowsing.makeAnchorCursor(sel);
-  } else {
-    return CaretBrowsing.makeFocusCursor(sel);
-  }
-};
-
-/**
- * Try to set the window's selection to be between the given start and end
- * cursors, and return whether or not it was successful.
- * @param {Cursor} start The start position.
- * @param {Cursor} end The end position.
- * @return {boolean} True if the selection was successfully set.
- */
-CaretBrowsing.setAndValidateSelection = function(start, end) {
-  var sel = window.getSelection();
-  sel.setBaseAndExtent(start.node, start.index, end.node, end.index);
-
-  if (sel.rangeCount != 1) {
-    return false;
-  }
-
-  return (sel.anchorNode == start.node &&
-          sel.anchorOffset == start.index &&
-          sel.focusNode == end.node &&
-          sel.focusOffset == end.index);
-};
-
-/**
- * Note: the built-in function by the same name is unreliable.
- * @param {Selection} sel The selection.
- * @return {boolean} True if the start and end positions are the same.
- */
-CaretBrowsing.isCollapsed = function(sel) {
-  return (sel.anchorOffset == sel.focusOffset &&
-          sel.anchorNode == sel.focusNode);
-};
-
-/**
- * Determines if the modifier key is held down that should cause
- * the cursor to move by word rather than by character.
- * @param {Event} evt A keyboard event.
- * @return {boolean} True if the cursor should move by word.
- */
-CaretBrowsing.isMoveByWordEvent = function(evt) {
-  if (CaretBrowsing.isMac) {
-    return evt.altKey;
-  } else {
-    return evt.ctrlKey;
-  }
-};
-
-/**
- * Moves the cursor forwards to the next valid position.
- * @param {Cursor} cursor The current cursor location.
- *     On exit, the cursor will be at the next position.
- * @param {Array.<Node>} nodesCrossed Any HTML nodes crossed between the
- *     initial and final cursor position will be pushed onto this array.
- * @return {?string} The character reached, or null if the bottom of the
- *     document has been reached.
- */
-CaretBrowsing.forwards = function(cursor, nodesCrossed) {
-  var previousCursor = cursor.clone();
-  var result = TraverseUtil.forwardsChar(cursor, nodesCrossed);
-
-  // Work around the fact that TraverseUtil.forwardsChar returns once per
-  // char in a block of text, rather than once per possible selection
-  // position in a block of text.
-  if (result && cursor.node != previousCursor.node && cursor.index > 0) {
-    cursor.index = 0;
-  }
-
-  return result;
-};
-
-/**
- * Moves the cursor backwards to the previous valid position.
- * @param {Cursor} cursor The current cursor location.
- *     On exit, the cursor will be at the previous position.
- * @param {Array.<Node>} nodesCrossed Any HTML nodes crossed between the
- *     initial and final cursor position will be pushed onto this array.
- * @return {?string} The character reached, or null if the top of the
- *     document has been reached.
- */
-CaretBrowsing.backwards = function(cursor, nodesCrossed) {
-  var previousCursor = cursor.clone();
-  var result = TraverseUtil.backwardsChar(cursor, nodesCrossed);
-
-  // Work around the fact that TraverseUtil.backwardsChar returns once per
-  // char in a block of text, rather than once per possible selection
-  // position in a block of text.
-  if (result &&
-      cursor.node != previousCursor.node &&
-      cursor.index < cursor.text.length) {
-    cursor.index = cursor.text.length;
-  }
-
-  return result;
-};
-
-/**
- * Called when the user presses the right arrow. If there's a selection,
- * moves the cursor to the end of the selection range. If it's a cursor,
- * moves past one character.
- * @param {Event} evt The DOM event.
- * @return {boolean} True if the default action should be performed.
- */
-CaretBrowsing.moveRight = function(evt) {
-  CaretBrowsing.targetX = null;
-
-  var sel = window.getSelection();
-  if (!evt.shiftKey && !CaretBrowsing.isCollapsed(sel)) {
-    var right = CaretBrowsing.makeRightCursor(sel);
-    CaretBrowsing.setAndValidateSelection(right, right);
-    return false;
-  }
-
-  var start = CaretBrowsing.isAmbiguous(sel) ?
-              CaretBrowsing.makeLeftCursor(sel) :
-              CaretBrowsing.makeAnchorCursor(sel);
-  var end = CaretBrowsing.isAmbiguous(sel) ?
-            CaretBrowsing.makeRightCursor(sel) :
-            CaretBrowsing.makeFocusCursor(sel);
-  var previousEnd = end.clone();
-  var nodesCrossed = [];
-  while (true) {
-    var result;
-    if (CaretBrowsing.isMoveByWordEvent(evt)) {
-      result = TraverseUtil.getNextWord(previousEnd, end, nodesCrossed);
-    } else {
-      previousEnd = end.clone();
-      result = CaretBrowsing.forwards(end, nodesCrossed);
-    }
-
-    if (result === null) {
-      return CaretBrowsing.moveLeft(evt);
-    }
-
-    if (CaretBrowsing.setAndValidateSelection(
-            evt.shiftKey ? start : end, end)) {
-      break;
-    }
-  }
-
-  if (!evt.shiftKey) {
-    nodesCrossed.push(end.node);
-    CaretBrowsing.setFocusToFirstFocusable(nodesCrossed);
-  }
-
-  return false;
-};
-
-/**
- * Called when the user presses the left arrow. If there's a selection,
- * moves the cursor to the start of the selection range. If it's a cursor,
- * moves backwards past one character.
- * @param {Event} evt The DOM event.
- * @return {boolean} True if the default action should be performed.
- */
-CaretBrowsing.moveLeft = function(evt) {
-  CaretBrowsing.targetX = null;
-
-  var sel = window.getSelection();
-  if (!evt.shiftKey && !CaretBrowsing.isCollapsed(sel)) {
-    var left = CaretBrowsing.makeLeftCursor(sel);
-    CaretBrowsing.setAndValidateSelection(left, left);
-    return false;
-  }
-
-  var start = CaretBrowsing.isAmbiguous(sel) ?
-              CaretBrowsing.makeLeftCursor(sel) :
-              CaretBrowsing.makeFocusCursor(sel);
-  var end = CaretBrowsing.isAmbiguous(sel) ?
-            CaretBrowsing.makeRightCursor(sel) :
-            CaretBrowsing.makeAnchorCursor(sel);
-  var previousStart = start.clone();
-  var nodesCrossed = [];
-  while (true) {
-    var result;
-    if (CaretBrowsing.isMoveByWordEvent(evt)) {
-      result = TraverseUtil.getPreviousWord(
-          start, previousStart, nodesCrossed);
-    } else {
-      previousStart = start.clone();
-      result = CaretBrowsing.backwards(start, nodesCrossed);
-    }
-
-    if (result === null) {
-      break;
-    }
-
-    if (CaretBrowsing.setAndValidateSelection(
-            evt.shiftKey ? end : start, start)) {
-      break;
-    }
-  }
-
-  if (!evt.shiftKey) {
-    nodesCrossed.push(start.node);
-    CaretBrowsing.setFocusToFirstFocusable(nodesCrossed);
-  }
-
-  return false;
-};
-
-
-/**
- * Called when the user presses the down arrow. If there's a selection,
- * moves the cursor to the end of the selection range. If it's a cursor,
- * attempts to move to the equivalent horizontal pixel position in the
- * subsequent line of text. If this is impossible, go to the first character
- * of the next line.
- * @param {Event} evt The DOM event.
- * @return {boolean} True if the default action should be performed.
- */
-CaretBrowsing.moveDown = function(evt) {
-  var sel = window.getSelection();
-  if (!evt.shiftKey && !CaretBrowsing.isCollapsed(sel)) {
-    var right = CaretBrowsing.makeRightCursor(sel);
-    CaretBrowsing.setAndValidateSelection(right, right);
-    return false;
-  }
-
-  var start = CaretBrowsing.isAmbiguous(sel) ?
-              CaretBrowsing.makeLeftCursor(sel) :
-              CaretBrowsing.makeAnchorCursor(sel);
-  var end = CaretBrowsing.isAmbiguous(sel) ?
-            CaretBrowsing.makeRightCursor(sel) :
-            CaretBrowsing.makeFocusCursor(sel);
-  var endRect = CaretBrowsing.getCursorRect(end);
-  if (CaretBrowsing.targetX === null) {
-    CaretBrowsing.targetX = endRect.left;
-  }
-  var previousEnd = end.clone();
-  var leftPos = end.clone();
-  var rightPos = end.clone();
-  var bestPos = null;
-  var bestY = null;
-  var bestDelta = null;
-  var bestHeight = null;
-  var nodesCrossed = [];
-  var y = -1;
-  while (true) {
-    if (null === CaretBrowsing.forwards(rightPos, nodesCrossed)) {
-      if (CaretBrowsing.setAndValidateSelection(
-            evt.shiftKey ? start : leftPos, leftPos)) {
-        break;
-      } else {
-        return CaretBrowsing.moveLeft(evt);
-      }
-      break;
-    }
-    var range = document.createRange();
-    range.setStart(leftPos.node, leftPos.index);
-    range.setEnd(rightPos.node, rightPos.index);
-    var rect = range.getBoundingClientRect();
-    if (rect && rect.width < rect.height) {
-      y = rect.top + window.pageYOffset;
-
-      // Return the best match so far if we get half a line past the best.
-      if (bestY != null && y > bestY + bestHeight / 2) {
-        if (CaretBrowsing.setAndValidateSelection(
-                evt.shiftKey ? start : bestPos, bestPos)) {
-          break;
-        } else {
-          bestY = null;
-        }
-      }
-
-      // Stop here if we're an entire line the wrong direction
-      // (for example, we reached the top of the next column).
-      if (y < endRect.top - endRect.height) {
-        if (CaretBrowsing.setAndValidateSelection(
-                evt.shiftKey ? start : leftPos, leftPos)) {
-          break;
-        }
-      }
-
-      // Otherwise look to see if this current position is on the
-      // next line and better than the previous best match, if any.
-      if (y >= endRect.top + endRect.height) {
-        var deltaLeft = Math.abs(CaretBrowsing.targetX - rect.left);
-        if ((bestDelta == null || deltaLeft < bestDelta) &&
-            (leftPos.node != end.node || leftPos.index != end.index)) {
-          bestPos = leftPos.clone();
-          bestY = y;
-          bestDelta = deltaLeft;
-          bestHeight = rect.height;
-        }
-        var deltaRight = Math.abs(CaretBrowsing.targetX - rect.right);
-        if (bestDelta == null || deltaRight < bestDelta) {
-          bestPos = rightPos.clone();
-          bestY = y;
-          bestDelta = deltaRight;
-          bestHeight = rect.height;
-        }
-
-        // Return the best match so far if the deltas are getting worse,
-        // not better.
-        if (bestDelta != null &&
-            deltaLeft > bestDelta &&
-            deltaRight > bestDelta) {
-          if (CaretBrowsing.setAndValidateSelection(
-                  evt.shiftKey ? start : bestPos, bestPos)) {
-            break;
-          } else {
-            bestY = null;
-          }
-        }
-      }
-    }
-    leftPos = rightPos.clone();
-  }
-
-  if (!evt.shiftKey) {
-    CaretBrowsing.setFocusToNode(leftPos.node);
-  }
-
-  return false;
-};
-
-/**
- * Called when the user presses the up arrow. If there's a selection,
- * moves the cursor to the start of the selection range. If it's a cursor,
- * attempts to move to the equivalent horizontal pixel position in the
- * previous line of text. If this is impossible, go to the last character
- * of the previous line.
- * @param {Event} evt The DOM event.
- * @return {boolean} True if the default action should be performed.
- */
-CaretBrowsing.moveUp = function(evt) {
-  var sel = window.getSelection();
-  if (!evt.shiftKey && !CaretBrowsing.isCollapsed(sel)) {
-    var left = CaretBrowsing.makeLeftCursor(sel);
-    CaretBrowsing.setAndValidateSelection(left, left);
-    return false;
-  }
-
-  var start = CaretBrowsing.isAmbiguous(sel) ?
-              CaretBrowsing.makeLeftCursor(sel) :
-              CaretBrowsing.makeFocusCursor(sel);
-  var end = CaretBrowsing.isAmbiguous(sel) ?
-            CaretBrowsing.makeRightCursor(sel) :
-            CaretBrowsing.makeAnchorCursor(sel);
-  var startRect = CaretBrowsing.getCursorRect(start);
-  if (CaretBrowsing.targetX === null) {
-    CaretBrowsing.targetX = startRect.left;
-  }
-  var previousStart = start.clone();
-  var leftPos = start.clone();
-  var rightPos = start.clone();
-  var bestPos = null;
-  var bestY = null;
-  var bestDelta = null;
-  var bestHeight = null;
-  var nodesCrossed = [];
-  var y = 999999;
-  while (true) {
-    if (null === CaretBrowsing.backwards(leftPos, nodesCrossed)) {
-      CaretBrowsing.setAndValidateSelection(
-          evt.shiftKey ? end : rightPos, rightPos);
-      break;
-    }
-    var range = document.createRange();
-    range.setStart(leftPos.node, leftPos.index);
-    range.setEnd(rightPos.node, rightPos.index);
-    var rect = range.getBoundingClientRect();
-    if (rect && rect.width < rect.height) {
-      y = rect.top + window.pageYOffset;
-
-      // Return the best match so far if we get half a line past the best.
-      if (bestY != null && y < bestY - bestHeight / 2) {
-        if (CaretBrowsing.setAndValidateSelection(
-                evt.shiftKey ? end : bestPos, bestPos)) {
-          break;
-        } else {
-          bestY = null;
-        }
-      }
-
-      // Exit if we're an entire line the wrong direction
-      // (for example, we reached the bottom of the previous column.)
-      if (y > startRect.top + startRect.height) {
-        if (CaretBrowsing.setAndValidateSelection(
-                evt.shiftKey ? end : rightPos, rightPos)) {
-          break;
-        }
-      }
-
-      // Otherwise look to see if this current position is on the
-      // next line and better than the previous best match, if any.
-      if (y <= startRect.top - startRect.height) {
-        var deltaLeft = Math.abs(CaretBrowsing.targetX - rect.left);
-        if (bestDelta == null || deltaLeft < bestDelta) {
-          bestPos = leftPos.clone();
-          bestY = y;
-          bestDelta = deltaLeft;
-          bestHeight = rect.height;
-        }
-        var deltaRight = Math.abs(CaretBrowsing.targetX - rect.right);
-        if ((bestDelta == null || deltaRight < bestDelta) &&
-            (rightPos.node != start.node || rightPos.index != start.index)) {
-          bestPos = rightPos.clone();
-          bestY = y;
-          bestDelta = deltaRight;
-          bestHeight = rect.height;
-        }
-
-        // Return the best match so far if the deltas are getting worse,
-        // not better.
-        if (bestDelta != null &&
-            deltaLeft > bestDelta &&
-            deltaRight > bestDelta) {
-          if (CaretBrowsing.setAndValidateSelection(
-                  evt.shiftKey ? end : bestPos, bestPos)) {
-            break;
-          } else {
-            bestY = null;
-          }
-        }
-      }
-    }
-    rightPos = leftPos.clone();
-  }
-
-  if (!evt.shiftKey) {
-    CaretBrowsing.setFocusToNode(rightPos.node);
-  }
-
-  return false;
-};
-
-/**
- * Set the document's selection to surround a control, so that the next
- * arrow key they press will allow them to explore the content before
- * or after a given control.
- * @param {Node} control The control to escape from.
- */
-CaretBrowsing.escapeFromControl = function(control) {
-  control.blur();
-
-  var start = new Cursor(control, 0, '');
-  var previousStart = start.clone();
-  var end = new Cursor(control, 0, '');
-  var previousEnd = end.clone();
-
-  var nodesCrossed = [];
-  while (true) {
-    if (null === CaretBrowsing.backwards(start, nodesCrossed)) {
-      break;
-    }
-
-    var r = document.createRange();
-    r.setStart(start.node, start.index);
-    r.setEnd(previousStart.node, previousStart.index);
-    if (r.getBoundingClientRect()) {
-      break;
-    }
-    previousStart = start.clone();
-  }
-  while (true) {
-    if (null === CaretBrowsing.forwards(end, nodesCrossed)) {
-      break;
-    }
-    if (isDescendantOfNode(end.node, control)) {
-      previousEnd = end.clone();
-      continue;
-    }
-
-    var r = document.createRange();
-    r.setStart(previousEnd.node, previousEnd.index);
-    r.setEnd(end.node, end.index);
-    if (r.getBoundingClientRect()) {
-      break;
-    }
-  }
-
-  if (!isDescendantOfNode(previousStart.node, control)) {
-    start = previousStart.clone();
-  }
-
-  if (!isDescendantOfNode(previousEnd.node, control)) {
-    end = previousEnd.clone();
-  }
-
-  CaretBrowsing.setAndValidateSelection(start, end);
-
-  window.setTimeout(function() {
-    CaretBrowsing.updateCaretOrSelection(true);
-  }, 0);
-};
-
-/**
- * Toggle whether caret browsing is enabled or not.
- */
-CaretBrowsing.toggle = function() {
-  if (CaretBrowsing.forceEnabled) {
-    CaretBrowsing.recreateCaretElement();
-    return;
-  }
-
-  CaretBrowsing.isEnabled = !CaretBrowsing.isEnabled;
-  var obj = {};
-  obj['enabled'] = CaretBrowsing.isEnabled;
-  chrome.storage.sync.set(obj);
-  CaretBrowsing.updateIsCaretVisible();
-};
-
-/**
- * Event handler, called when a key is pressed.
- * @param {Event} evt The DOM event.
- * @return {boolean} True if the default action should be performed.
- */
-CaretBrowsing.onKeyDown = function(evt) {
-  if (evt.defaultPrevented) {
-    return;
-  }
-
-  if (evt.keyCode == 118) {  // F7
-    CaretBrowsing.toggle();
-  }
-
-  if (!CaretBrowsing.isEnabled) {
-    return true;
-  }
-
-  if (evt.target && CaretBrowsing.isControlThatNeedsArrowKeys(
-      /** @type (Node) */(evt.target))) {
-    if (evt.keyCode == 27) {
-      CaretBrowsing.escapeFromControl(/** @type {Node} */(evt.target));
-      evt.preventDefault();
-      evt.stopPropagation();
-      return false;
-    } else {
-      return true;
-    }
-  }
-
-  // If the current selection doesn't have a range, try to escape out of
-  // the current control. If that fails, return so we don't fail whe
-  // trying to move the cursor or selection.
-  var sel = window.getSelection();
-  if (sel.rangeCount == 0) {
-    if (document.activeElement) {
-      CaretBrowsing.escapeFromControl(document.activeElement);
-      sel = window.getSelection();
-    }
-
-    if (sel.rangeCount == 0) {
-      return true;
-    }
-  }
-
-  if (CaretBrowsing.caretElement) {
-    CaretBrowsing.caretElement.style.visibility = 'visible';
-    CaretBrowsing.blinkFlag = true;
-  }
-
-  var result = true;
-  switch (evt.keyCode) {
-    case 37:
-      result = CaretBrowsing.moveLeft(evt);
-      break;
-    case 38:
-      result = CaretBrowsing.moveUp(evt);
-      break;
-    case 39:
-      result = CaretBrowsing.moveRight(evt);
-      break;
-    case 40:
-      result = CaretBrowsing.moveDown(evt);
-      break;
-  }
-
-  if (result == false) {
-    evt.preventDefault();
-    evt.stopPropagation();
-  }
-
-  window.setTimeout(function() {
-    CaretBrowsing.updateCaretOrSelection(result == false);
-  }, 0);
-
-  return result;
-};
-
-/**
- * Event handler, called when the mouse is clicked. Chrome already
- * sets the selection when the mouse is clicked, all we need to do is
- * update our cursor.
- * @param {Event} evt The DOM event.
- * @return {boolean} True if the default action should be performed.
- */
-CaretBrowsing.onClick = function(evt) {
-  if (!CaretBrowsing.isEnabled) {
-    return true;
-  }
-  window.setTimeout(function() {
-    CaretBrowsing.targetX = null;
-    CaretBrowsing.updateCaretOrSelection(false);
-  }, 0);
-  return true;
-};
-
-/**
- * Called at a regular interval. Blink the cursor by changing its visibility.
- */
-CaretBrowsing.caretBlinkFunction = function() {
-  if (CaretBrowsing.caretElement) {
-    if (CaretBrowsing.blinkFlag) {
-      CaretBrowsing.caretElement.style.backgroundColor =
-          CaretBrowsing.caretForeground;
-      CaretBrowsing.blinkFlag = false;
-    } else {
-      CaretBrowsing.caretElement.style.backgroundColor =
-          CaretBrowsing.caretBackground;
-      CaretBrowsing.blinkFlag = true;
-    }
-  }
-};
-
-/**
- * Update whether or not the caret is visible, based on whether caret browsing
- * is enabled and whether this window / iframe has focus.
- */
-CaretBrowsing.updateIsCaretVisible = function() {
-  CaretBrowsing.isCaretVisible =
-      (CaretBrowsing.isEnabled && CaretBrowsing.isWindowFocused);
-  if (CaretBrowsing.isCaretVisible && !CaretBrowsing.caretElement) {
-    CaretBrowsing.setInitialCursor();
-    CaretBrowsing.updateCaretOrSelection(true);
-    if (CaretBrowsing.caretElement) {
-      CaretBrowsing.blinkFunctionId = window.setInterval(
-          CaretBrowsing.caretBlinkFunction, 500);
-    }
-  } else if (!CaretBrowsing.isCaretVisible &&
-             CaretBrowsing.caretElement) {
-    window.clearInterval(CaretBrowsing.blinkFunctionId);
-    if (CaretBrowsing.caretElement) {
-      CaretBrowsing.isSelectionCollapsed = false;
-      CaretBrowsing.caretElement.parentElement.removeChild(
-          CaretBrowsing.caretElement);
-      CaretBrowsing.caretElement = null;
-    }
-  }
-};
-
-/**
- * Called when the prefs get updated.
- */
-CaretBrowsing.onPrefsUpdated = function() {
-  chrome.storage.sync.get(null, function(result) {
-    if (!CaretBrowsing.forceEnabled) {
-      CaretBrowsing.isEnabled = result['enabled'];
-    }
-    CaretBrowsing.onEnable = result['onenable'];
-    CaretBrowsing.onJump = result['onjump'];
-    CaretBrowsing.recreateCaretElement();
-  });
-};
-
-/**
- * Called when this window / iframe gains focus.
- */
-CaretBrowsing.onWindowFocus = function() {
-  CaretBrowsing.isWindowFocused = true;
-  CaretBrowsing.updateIsCaretVisible();
-};
-
-/**
- * Called when this window / iframe loses focus.
- */
-CaretBrowsing.onWindowBlur = function() {
-  CaretBrowsing.isWindowFocused = false;
-  CaretBrowsing.updateIsCaretVisible();
-};
-
-/**
- * Initializes caret browsing by adding event listeners and extension
- * message listeners.
- */
-CaretBrowsing.init = function() {
-  CaretBrowsing.isWindowFocused = document.hasFocus();
-
-  document.addEventListener('keydown', CaretBrowsing.onKeyDown, false);
-  document.addEventListener('click', CaretBrowsing.onClick, false);
-  window.addEventListener('focus', CaretBrowsing.onWindowFocus, false);
-  window.addEventListener('blur', CaretBrowsing.onWindowBlur, false);
-};
-
-window.setTimeout(function() {
-
-  // Make sure the script only loads once.
-  if (!window['caretBrowsingLoaded']) {
-    window['caretBrowsingLoaded'] = true;
-    CaretBrowsing.init();
-
-    if (document.body.getAttribute('caretbrowsing') == 'on') {
-      CaretBrowsing.forceEnabled = true;
-      CaretBrowsing.isEnabled = true;
-      CaretBrowsing.updateIsCaretVisible();
-    }
-
-    chrome.storage.onChanged.addListener(function() {
-      CaretBrowsing.onPrefsUpdated();
-    });
-    CaretBrowsing.onPrefsUpdated();
-  }
-
-}, 0);