bug#63438: 30.0.50; abbrev mode wrongly capitalizes with mixed capitalized words

[Eli Zaretskii <eliz@gnu.org>]

severity 63438 wishlist
thanks

> From: Daniel Fleischer <danflscr@gmail.com>
> Date: Thu, 11 May 2023 10:10:40 +0300
> 
> Recipe for recreating:
> 
> - Add some abbrev definition with mixed capitalization, e.g. "abc"
> should expand to "aBC".
> - Enable abbrev-mode. 
> - Write "aBC".
> - Upon pressing space, abbrev-mode converts it into "ABC". 
> 
> There is a code section in `abbrev-insert' that explicitly capitalizes
> the first letter; I'm sure it's there for a reason but I think the
> behavior I showed is unexpected. As for the example "aBC", there are
> real use cases, just to mention one "iPhone".

What you see is the documented behavior: by default, if the abbrev was
triggered by a word that has some upper-case letters in it, Emacs
capitalizes the first letter of every word in the expansion (you can
optionally set abbrev-all-caps non-nil to up-case all the letters in
the expansion).  In your case, capitalizing the first letter of "aBC"
yields "ABC", and that's what you see.

What did you expect to happen instead?