private static function _mime_extension(string $fname) {
		$pinfo = pathinfo($fname);
		// @codeCoverageIgnoreStart
		if (!isset($pinfo['extension']))
			return null;
		// @codeCoverageIgnoreEnd
		# Because these things are magically ambiguous, we'll
		# resort to extension.
		switch (strtolower($pinfo['extension'])) {
			case 'css':
				return 'text/css';
			case 'js':
				return 'application/javascript';
			case 'json':
				return 'application/json';
			case 'htm':
			case 'html':
				# always assume UTF-8
				return 'text/html; charset=utf-8';
		}
		return null;
	}