HTML Template Language (HTL) block statements are custom data attributes added directly to existing HTML. This allows easy and unobtrusive annotation of a prototype static HTML page, converting it to a functioning dynamic template without breaking the validity of the HTML code.
The element does not get displayed in the resulting HTML and can be used instead of the data-sly-unwrap. The goal of the element is to make it more obvious that the element is not outputted. If you want you can still use data-sly-unwrap.