1 files changed, 9 insertions, 4 deletions

diff --git a/src/dispextern.h b/src/dispextern.h
index 55fd852ea3b..3b24d49da75 100644
--- a/src/dispextern.h
+++ b/src/dispextern.h
@@ -321,13 +321,18 @@ struct glyph
      Lisp string, this is a position in that string.  If it is a
      buffer, this is a position in that buffer.  A value of -1
      together with a null object means glyph is a truncation glyph at
-     the start of a row.  */
+     the start of a row.  Right truncation and continuation glyphs at
+     the right edge of a row have their position set to the next
+     buffer position that is not shown on this row.  Glyphs inserted
+     by redisplay, such as the empty space after the end of a line on
+     TTYs, or the overlay-arrow on a TTY, have this set to -1.  */
   ptrdiff_t charpos;
 
-  /* Lisp object source of this glyph.  Currently either a buffer or
-     a string, if the glyph was produced from characters which came from
+  /* Lisp object source of this glyph.  Currently either a buffer or a
+     string, if the glyph was produced from characters which came from
      a buffer or a string; or 0 if the glyph was inserted by redisplay
-     for its own purposes such as padding.  */
+     for its own purposes, such as padding or truncation/continuation
+     glyphs, or the overlay-arrow glyphs on TTYs.  */
   Lisp_Object object;
 
   /* Width in pixels.  */