Thisbusiness with a textual representation of a sort clause seems like over-engineering ... except that it's also under-engineered, because the parsing is lame and incomplete. (No USING option, and the fact that collation comes from somewhere else seems impossibly confusing.) Let's drop that.
I can accept this outcome though an optional three-valued boolean sort order (ascending and descending only) I'd argue is worth keeping. null value placement too I guess, three-valued boolean (nulls_first).
