emacs-28 195fcc932e: Improve the documentation of glyphless-character display

[Eli Zaretskii]

branch: emacs-28
commit 195fcc932eea396c94483e0265b43a3c01147776
Author: Eli Zaretskii <eliz@gnu.org>
Commit: Eli Zaretskii <eliz@gnu.org>

    Improve the documentation of glyphless-character display
    
    * lisp/international/characters.el (glyphless-char-display-control):
    * src/xdisp.c (syms_of_xdisp) <glyphless-char-display>: Mention
    the 'glyphless-char' face in the doc string.
    
    * doc/lispref/display.texi (Glyphless Chars): Index
    'glyphless-char' face.
---
 doc/lispref/display.texi         | 4 +++-
 lisp/international/characters.el | 8 ++++++--
 src/xdisp.c                      | 3 +++
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index 9aed5b2d7a..b068c7d08c 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -7994,6 +7994,7 @@ Display with @var{graphical} on graphical displays, and 
with
 must be one of the display methods described above.
 @end table
 
+@vindex glyphless-char@r{ face}
 @noindent
 The @code{thin-space}, @code{empty-box}, @code{hex-code}, and
 @acronym{ASCII} string display methods are drawn with the
@@ -8048,7 +8049,8 @@ emojis).
 
 @item no-font
 Characters for which there is no suitable font, or which cannot be
-encoded by the terminal's coding system.
+encoded by the terminal's coding system, or those for which the
+text-mode terminal has no glyphs.
 @end table
 
 @c FIXME: this can also be 'acronym', but that's not currently
diff --git a/lisp/international/characters.el b/lisp/international/characters.el
index 7d625d1382..d845baa2eb 100644
--- a/lisp/international/characters.el
+++ b/lisp/international/characters.el
@@ -1599,7 +1599,8 @@ GROUP must be one of these symbols:
                          presentation).
   `no-font':        characters for which no suitable font is found.
                     For character terminals, characters that cannot
-                    be encoded by `terminal-coding-system'.
+                    be encoded by `terminal-coding-system' or those
+                    for which the terminal has no glyphs.
 
 METHOD must be one of these symbols:
   `zero-width': don't display.
@@ -1613,7 +1614,10 @@ METHOD must be one of these symbols:
 Do not set its value directly from Lisp; the value takes effect
 only via a custom `:set'
 function (`update-glyphless-char-display'), which updates
-`glyphless-char-display'."
+`glyphless-char-display'.
+
+See also the `glyphless-char' face, which is used to display the
+visual representation of these characters."
   :version "28.1"
   :type '(alist :key-type (symbol :tag "Character Group")
                :value-type (symbol :tag "Display Method"))
diff --git a/src/xdisp.c b/src/xdisp.c
index a4881c4835..6d42105474 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -35831,6 +35831,9 @@ which no font is found on graphical terminals, and 
characters that cannot
 be displayed by text-mode terminals.  Its value should be an ASCII acronym
 string, `hex-code', `empty-box', or `thin-space'.  The default is `hex-code'.
 
+With the obvious exception of `zero-width', all the other representations
+are displayed using the face `glyphless-char'.
+
 If a character has a non-nil entry in an active display table, the
 display table takes effect; in this case, Emacs does not consult
 `glyphless-char-display' at all.  */);