Also there is the tag <lfr-widget-[Widget/Portlet alias]></lfr-widget-[Widget/Portlet alias]> to embed Widgets (Portlets), to make it work you have to add the portlet alias to the tag.
Let's think you'd like to embed a breadcrumb widget into a Page Fragment, you tag should be something like:
According to the W3C HTML standards, custom elements cannot be self closing. Therefore, even though you cannot add anything between the opening and closing <lfr-widget...> tags, you cannot use the self closing notation for the tag. (Liferay references).
If you want to know about fragment tags, please click here.