Re: Uppercase character predicate

On Fri, Aug 14, 2026 at 10:22 AM Eli Zaretskii <[email protected]> wrote:
>
> > From: Stephen Berman <[email protected]>
> > Cc: Nikolaos Chatzikonstantinou <[email protected]>,  [email protected]
> > Date: Fri, 14 Aug 2026 13:48:34 +0200
> >
> > On Fri, 14 Aug 2026 14:28:29 +0300 Eli Zaretskii <[email protected]> wrote:
> >
> > >> From: Nikolaos Chatzikonstantinou <[email protected]>
> > >> Date: Thu, 13 Aug 2026 23:08:40 -0400
> > >>
> > >> Hello list,
> > >>
> > >> I tried using the `char-uppercase-p' with the MATHEMATICAL FRAKTUR
> > >> CAPITAL A character (unicode #x1d504) but it evaluated to nil. I
> > >> peeked through `describe-char' to see how it comes up with the
> > >> description above (since I can use it to detect if a character is
> > >> capital) and I came up with this:
> > >>
> > >>   (defun my/upcase-p (ch)
> > >>     "Check if CH is uppercase.
> > >>
> > >>   Slower, but more accurate than `char-uppercase-p'."
> > >>     (string-match-p "CAPITAL"
> > >>                     (get-char-code-property ch 'name)))
> > >>
> > >> This function works for my needs, but why doesn't `char-uppercase-p'
> > >> evaluate to true for this character?
> > >
> > > Because Emacs considers a character to be uppercase only if there's a
> > > corresponding lowercase character which makes the upper-/lower-case
> > > pair.  And MATHEMATICAL FRAKTUR CAPITAL A doesn't have a corresponding
> > > lowercase character.
> >
> > Why doesn't MATHEMATICAL FRAKTUR SMALL A (#x1d51e) fit that bill?
> >
> > (get-char-code-property #x1d504 'general-category) => Lu
> > (get-char-code-property #x1d51e 'general-category) => Ll
>
> Because Unicode database doesn't specify them as a case pair.

Some more details in
<https://www.unicode.org/faq/casemap_charprop.html#casemap>.  I think
that I understood the issue: the character is considered only as a
math symbol by Unicode, not an alphabet letter. (I also use them only
as math symbols.)

PS. Thanks for that code snippet Eli!
PPS. I accidentally sent 2 e-mails to some recipients.

-- 
Regards,
Nikolaos Chatzikonstantinou