@assets directive is a shorthand directive that loads static files directly from the
assets folder which is a subdirectory of the res/ folder. This directive can also be applied
to load grouped static files just like the @Res() method. The example below shows how this directive can be applied in template files
@assets('css/file.css') // <link href="{domain}/res/assets/css/file.css"/>
@assets(':headers') // import headers