original_string: public function at($start = null, $length = null)
      {
          return new String(mb_substr((string) $this, $start, $length, 'UTF-8'));
      }
code: public function at($start = null, $length = null)
      {
          return new String(mb_substr((string) $this, $start, $length, 'UTF-8'));
      }
code_tokens: public function at ( $ start = null , $ length = null ) { return new String ( mb_substr ( ( string ) $ this , $ start , $ length , 'UTF-8' ) ) ; }
docstring: Returns part of a string
  
  @param integer start
  @param  integer   $length the length of the string from the starting point
  @return PO\String
docstring_tokens: Returns part of a string