protected function _eatWhitespace()
    {
        if (preg_match(
            '/([\t\b\f\n\r ])*/s',
            $this->_source,
            $matches,
            PREG_OFFSET_CAPTURE,
            $this->_offset
        )
            && $matches[0][1] == $this->_offset
        ) {
            $this->_offset += strlen($matches[0][0]);
        }
    }