Re: Uppercase character predicate

> 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.

And even if you want to get rid of that prerequisite, for some reason,
your implementation is incorrect.  You should do this instead:

    (defun my/upcase-p (ch)
      "Check if CH is an uppercase character."
      (eq 'Lu (get-char-code-property ch 'general-category)))