emacs-27 f750def: Mention in PROBLEMS the problems with fonts and Uniscribe

[Eli Zaretskii]

branch: emacs-27
commit f750def7785a548d4be3aa27071ac47219f7a4e2
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Mention in PROBLEMS the problems with fonts and Uniscribe
    
    * etc/PROBLEMS: Mention font-related problems with Uniscribe on
    MS-Windows.  (Bug#39340)
---
 etc/PROBLEMS | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/etc/PROBLEMS b/etc/PROBLEMS
index 12cfbd0..32ac715 100644
--- a/etc/PROBLEMS
+++ b/etc/PROBLEMS
@@ -918,6 +918,19 @@ index 5504171..431adf8 100644
 If you can't modify that file directly, copy it to the directory
 ~/.m17n.d/ (create it if it doesn't exist), and apply the patch.
 
+** On MS-Windows, some characters display as boxes with hex code.
+
+Also, some characters could display with wrong fonts.
+
+This can happen if Emacs was compiled without HarfBuzz support, and/or
+if the HarfBuzz DLLs are not available at run time.  Emacs will then
+fall back to the Uniscribe as its shaping engine; Uniscribe was
+deprecated by Microsoft, and sometimes fails to display correctly when
+modern fonts are used, such as Noto Emoji or Ebrima.
+
+The solution is to switch to a configuration that uses HarfBuzz as its
+shaping engine, where these problems don't exist.
+
 * Internationalization problems
 
 ** M-{ does not work on a Spanish PC keyboard.