code: function(p_sType, p_aArgs) {
              if (!this.firstElement) {
                  if (UA.webkit || UA.opera) {
                      if (!this._modalFocus) {
                          this._createHiddenFocusElement();
                      }
                  } else {
                      this.innerElement.tabIndex = 0;
                  }
              }
              this.setTabLoop(this.firstElement, this.lastElement);
              Event.onFocus(document.documentElement, this._onElementFocus, this, true);
              _currentModal = this;
          }
docs: @method _addFocusHandlers
  @protected
  
  "showMask" event handler that adds a "focus" event handler to all
  focusable elements in the document to enforce a Panel instance's
  modality from being compromised.
  
  @param p_sType {String} Custom event type
  @param p_aArgs {Array} Custom event arguments