/**
  * Selects a popup window; once a popup window has been selected,
  * all commands go to that window. To select the main window again,
  * use "null" as the target.
  *
  * @param  string  $windowId
  * @return string
  * @access public
  */
 public function selectWindow($windowId)
 {
     return $this->selenium->selectWindow($windowId);
 }