code: function _getDisplayKey(key) {
          var displayKey = "",
              match = key ? key.match(/(Up|Down|Left|Right|\-)$/i) : null;
          if (match && !/Page(Up|Down)/.test(key)) {
              displayKey = key.substr(0, match.index) + _displayKeyMap[match[0].toLowerCase()];
          }
          return displayKey;
      }
docs: @private
  
  Gets the corresponding unicode symbol of an arrow key for display in the menu.
  @param {string} key The non-modifier key used in the shortcut. It does not need to be normalized.
  @return {string} An empty string if key is not one of those we want to show with the unicode symbol.
  Otherwise, the corresponding unicode symbol is returned.