diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index bc18daa..e1ce00f 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -7218,6 +7218,9 @@
 				properties the one with the highest priority
 				will be used; negative values can be used, the
 				default priority is zero
+		   combine	when TRUE combine the highlight with any
+				syntax highlight; when omitted of FALSE syntax
+				highlight will not be used
 		   start_incl	when TRUE inserts at the start position will
 				be included in the text property
 		   end_incl	when TRUE inserts at the end position will be