patch 9.1.0936: cannot highlight completed text

Problem:  cannot highlight completed text
Solution: (optionally) highlight auto-completed text using the
          ComplMatchIns highlight group (glepnir)

closes: #16173

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 eb6c3b2..7640ee1 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 12
+*syntax.txt*	For Vim version 9.1.  Last change: 2024 Dec 16
 
 
 		  VIM REFERENCE MANUAL	  by Bram Moolenaar
@@ -5857,6 +5857,8 @@
 PmenuMatch	Popup menu: Matched text in normal item.
 							*hl-PmenuMatchSel*
 PmenuMatchSel	Popup menu: Matched text in selected item.
+							*hl-ComplMatchIns*
+ComplMatchIns	Matched text of the currently inserted completion.
 							*hl-PopupNotification*
 PopupNotification
 		Popup window created with |popup_notification()|.  If not