original_string: public function add_ref($item, $id) {
          $this->validate_item($item);
          $this->refs[$item][$id] = true;
      }
code: public function add_ref($item, $id) {
          $this->validate_item($item);
          $this->refs[$item][$id] = true;
      }
code_tokens: public function add_ref ( $ item , $ id ) { $ this -> validate_item ( $ item ) ; $ this -> refs [ $ item ] [ $ id ] = true ; }
docstring: Adds a reference
  
  @param string $item the name of referenced item (like user, file, scale, outcome or grade_item)
  @param int $id the value of the reference
docstring_tokens: Adds a reference