> For another application (upcoming Lisp Union documents), I solved that
> problem by trying to reduce Scribble to a minimal core.

The point of that format is to be "inverse S-expressions". Whereas in
S-expressions you write the tree structure by default and use
double-quotes to write free-form text, in this format you write
free-form text by default and use # to insert tree structure.

It's not intended to have anything else. By design, there is an
extremely predictable mapping from any document in this markup language
to an equivalent S-expression, so that the latter is as easy as possible
to post-process in Scheme/Lisp.