Form has `render_start` but block does not

[Altreus]

The default block widget just creates the <$tag> inside render, meaning you can't pull a block apart to manually render some of it, like you can with a form.

https://github.com/gshank/html-formhandler/blob/b62ac37421740b16ed0043e71d968606478335e5/lib/HTML/FormHandler/Widget/Block.pm#L130