original_string: public function at($start = null, $length = null)
      {
          return new self(mb_substr((string) $this, $start, $length, 'UTF-8'));
      }
code: public function at($start = null, $length = null)
      {
          return new self(mb_substr((string) $this, $start, $length, 'UTF-8'));
      }
code_tokens: public function at ( $ start = null , $ length = null ) { return new self ( mb_substr ( ( string ) $ this , $ start , $ length , 'UTF-8' ) ) ; }
docstring: Returns part of a string
  Known bug in php 5.3.3
  
  @see https://bugs.php.net/bug.php?id=62703
  
  @param int start
  @param int $length the length of the string from the starting point
  
  @return KoineString
docstring_tokens: Returns part of a string Known bug in php 5 . 3 . 3