Both Datastar and HTMX have the same issue: they want to pretend to be HTML. So they force themselves into writing several DSLs like this to pretend that this is still "just HTML".

Since they have a full "Datastar expression" language, I'd just expand that. Then you wouldn't need these weird constructs:

   <button data-on-click__window__debounce.500ms.leading="$foo = ''"></button>