/**
   * Tab key has been pressed inside a table cell.
   *
   * @param event the native event that was fired
   * @param cell The table cell in which the tab key has been pressed.
   */
  protected void onTabInTableCell(Event event, TableCellElement cell) {
    Node nextCell = event.getShiftKey() ? cell.getPreviousCell() : cell.getNextCell();
    if (nextCell == null) {
      if (event.getShiftKey()) {
        return;
      } else {
        getTextArea().getCommandManager().execute(new Command("insertrowafter"));
        nextCell = cell.getNextCell();
      }
    }

    Selection selection = getTextArea().getDocument().getSelection();
    Range range = selection.getRangeAt(0);

    // Place the caret at the beginning of the next cell.
    Node leaf = domUtils.getFirstLeaf(nextCell);
    if (leaf == nextCell || leaf.getNodeType() == Node.TEXT_NODE) {
      range.setStart(leaf, 0);
    } else {
      range.setStartBefore(leaf);
    }

    range.collapse(true);
    selection.removeAllRanges();
    selection.addRange(range);
  }
  /**
   * Inserts a paragraph before or after the table containing the selection.
   *
   * <p>We decided to use Control/Meta+UpArrow for inserting a paragraph before a table and
   * Control/Meta+DownArrow for inserting a paragraph after a table. Here's the rationale:
   *
   * <ul>
   *   <li>We can't reliably detect if the user can place the caret before of after a table. Our
   *       playground is the DOM tree which we fully control but in the end the browser decides how
   *       to render each node. The table can have previous siblings or previous nodes in the DOM
   *       tree but they may not be rendered at all (as it happens with HTML garbage like empty
   *       elements) or not rendered before/after the table (as it happens with absolute positioned
   *       elements). So we have to insert the paragraph each time.
   *   <li>We can't use the same key to insert a paragraph before and after the table because we can
   *       have a table with just one empty cell. So we can't rely on the Enter key.
   *   <li>We can't use just the navigation keys because they would insert a paragraph before/after
   *       the table even when the user can navigate outside of the table.
   * </ul>
   *
   * We can replace the Ctrl with Alt. The idea is to use the Up/Down arrow keys with a modifier.
   * They will work form any table cell.
   *
   * @param event the native event that was fired
   * @param before {@code true} to insert a paragraph before the table, {@code false} to insert a
   *     paragraph after the table
   */
  protected void navigateOutsideTableCell(Event event, boolean before) {
    // Navigate only if the Control or Meta modifiers are pressed along with the Up/Down arrow keys.
    if (event.getAltKey() || event.getShiftKey() || !(event.getCtrlKey() ^ event.getMetaKey())) {
      return;
    }

    Selection selection = getTextArea().getDocument().getSelection();
    if (selection.getRangeCount() == 0) {
      return;
    } else {
      selection.collapseToStart();
    }

    Range range = selection.getRangeAt(0);
    Node ancestor = domUtils.getFirstAncestor(range.getStartContainer(), "table");
    if (ancestor == null) {
      return;
    }

    event.xPreventDefault();

    Document document = getTextArea().getDocument();
    Node paragraph = document.createPElement();
    paragraph.appendChild(document.createTextNode(""));

    if (before) {
      ancestor.getParentNode().insertBefore(paragraph, ancestor);
    } else {
      domUtils.insertAfter(paragraph, ancestor);
    }

    range.selectNodeContents(paragraph.getFirstChild());
    selection.removeAllRanges();
    selection.addRange(range);
  }
 /**
  * Tab key has been pressed in an ordinary context. If the Shift key was not pressed then the
  * current selection will be replaced by 4 spaces. Otherwise no action will be taken.
  *
  * @param event the native event that was fired
  */
 protected void onTabDefault(Event event) {
   if (event.getShiftKey()) {
     // Do nothing.
   } else {
     if (getTextArea().getCommandManager().isEnabled(Command.INSERT_HTML)) {
       getTextArea().getCommandManager().execute(Command.INSERT_HTML, "&nbsp;&nbsp;&nbsp;&nbsp;");
       getTextArea().getDocument().getSelection().collapseToEnd();
     }
   }
 }
 /**
  * Tab key has been pressed inside a list item. If the selection is collapsed at the beginning of
  * a list item then indent or outdent that list item depending on the Shift key. Otherwise use the
  * default behavior for Tab key.
  *
  * @param event the native event that was fired
  * @param item the list item in which the tab key has been pressed
  */
 protected void onTabInListItem(Event event, Node item) {
   Range range = getTextArea().getDocument().getSelection().getRangeAt(0);
   if (!range.isCollapsed() || !isAtStart(item, range)) {
     onTabDefault(event);
   } else {
     Command command = event.getShiftKey() ? Command.OUTDENT : Command.INDENT;
     if (getTextArea().getCommandManager().isEnabled(command)) {
       getTextArea().getCommandManager().execute(command);
     }
   }
 }