public static function addToHTML()
    {
        if (!self::isViewingHTMLPage()) {
            return;
        }

        // js
        $paths = self::getAssetFilePaths('js');
        echo sprintf(
            '<script>%s</script>',
            self::getCombinedContents($paths)
        );

        // css
        $paths = self::getAssetFilePaths('css');
        echo sprintf(
            '<style>%s</style>',
            self::getCombinedContents($paths)
        );
    }