A lovely feature I added to my own language when I wrote one about a dozen years ago was the construct "not in", eg:
if Ch not in ['A'..'Z'] then ...
I always thought this was much nicer than the ugly:
if not (Ch in ['A'..'Z']) then
as well as much clearer.
I don't know if others agree, but if so it might be a nice extension for GPC.
Anyway, just thought I'd mention it since I happened to be working on the docs for "in" ;-)
Enjoy, Peter.