original_string: public function add($string)
      {
          $this->timestamp = $this->getTimestamp() + $this->evaluateDateString($string);
  
          return $this;
      }
code: public function add($string)
      {
          $this->timestamp = $this->getTimestamp() + $this->evaluateDateString($string);
  
          return $this;
      }
code_tokens: public function add ( $ string ) { $ this -> timestamp = $ this -> getTimestamp ( ) + $ this -> evaluateDateString ( $ string ) ; return $ this ; }
docstring: Add a specific period
  
  @param string $string The period to add
  
  @return DateTime
docstring_tokens: Add a specific period