diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index f621fc0..a9bba86 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -3928,6 +3928,8 @@
 			wincol		column inside "winid"
 			line		text line inside "winid"
 			column		text column inside "winid"
+			coladd		offset (in screen columns) from the
+					start of the clicked char
 		All numbers are 1-based.
 
 		If not over a window, e.g. when in the command line, then only