protected function _getClassCount($class)
    {
        $count = 0;
        if ($class == self::CLASS_LETTER) {
            $count = $this->_getClassCount(self::CLASS_LOWER)
                   + $this->_getClassCount(self::CLASS_UPPER);
        } else {
            if (isset ($this->_tokenCounts[$class])) {
                $count = $this->_tokenCounts[$class];
            }
        }

        return $count;
    }