public function checkSingleExtension($extension)
    {
        $extension = strtolower(ltrim($extension,'.'));

        if (sizeof($this->_deniedExtensions)) {
            if (in_array($extension, $this->_deniedExtensions)) {
                return false;
            }
        }

        if (sizeof($this->_allowedExtensions)) {
            return in_array($extension, $this->_allowedExtensions);
        }

        return true;
    }