Re: Uppercase character predicate

> 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.