Which leads us back to the question - did anyone of those who did that
over decades ever bothered to post some kind of "spec" for this
Is there a lot that needs to be specified? I imagine that the braces would correspond to the special INDENT and DEDENT tokens in the grammar and that's the bulk of the problem solved. The only remaining questions I can think of are whether you would want to keep the colons that initiate indented blocks and how to deal with ambiguity between the new blocks and existing uses of braces like set displays. Anything else?