code: protected function quoteLeading(/*# string */ $str)/*# : string */
      {
          $parts = preg_split('/([^0-9a-zA-Z_.])/', $str, 5,
              \PREG_SPLIT_DELIM_CAPTURE | \PREG_SPLIT_NO_EMPTY);
          $first = array_shift($parts);
          return $this->quote($first) . join('', $parts);
      }
docs: Quote 'name(4) ASC' as '`name`(4) ASC' as used in index creation
  @param  string $str
  @return string
  @access protected