patch 9.1.1006: PmenuMatch completion highlight can be combined

Problem:  PmenuMatch completion highlight can be combined
Solution: Combine highlight groups PmenuMatch with Pmenu and
          PmenuMatchSel with PmenuSel (glepnir)

fixes: #15563
closes: #16408

Signed-off-by: glepnir <glephunter@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/doc/syntax.txt b/runtime/doc/syntax.txt
index 7640ee1..2fb320e 100644
--- a/runtime/doc/syntax.txt
+++ b/runtime/doc/syntax.txt
@@ -1,4 +1,4 @@
-*syntax.txt*	For Vim version 9.1.  Last change: 2024 Dec 16
+*syntax.txt*	For Vim version 9.1.  Last change: 2025 Jan 11
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -5854,9 +5854,11 @@
 							*hl-PmenuThumb*
 PmenuThumb	Popup menu: Thumb of the scrollbar.
 							*hl-PmenuMatch*
-PmenuMatch	Popup menu: Matched text in normal item.
+PmenuMatch	Popup menu: Matched text in normal item. Applied in
+		combination with |hl-Pmenu|.
 							*hl-PmenuMatchSel*
-PmenuMatchSel	Popup menu: Matched text in selected item.
+PmenuMatchSel	Popup menu: Matched text in selected item. Applied in
+		combination with |hl-PmenuSel|.
 							*hl-ComplMatchIns*
 ComplMatchIns	Matched text of the currently inserted completion.
 							*hl-PopupNotification*