code: public function bind($key, & $value) {
          $this->open();
  
          $this->_data[$key] =& $value;
  
          return $this;
      }
docs: Set a variable by reference.
  
  $session->bind('foo', $foo);
  
  @param   string $key variable name
  @param   mixed $value referenced value
  @return  $this