protected function _code($str) {
		$self=$this;
		return preg_replace_callback(
			'/`` (.+?) ``|(?<!\\\\)`(.+?)(?!\\\\)`/',
			function($expr) use($self) {
				return '<code>'.
					$self->esc(empty($expr[1])?$expr[2]:$expr[1]).'</code>';
			},
			$str
		);
	}