diff --git a/runtime/doc/builtin.txt b/runtime/doc/builtin.txt
index 8855dd0..cf48b4d 100644
--- a/runtime/doc/builtin.txt
+++ b/runtime/doc/builtin.txt
@@ -806,9 +806,10 @@
 
 		For the use of {buf}, see |bufname()|.
 
-		{lnum} is used like with |append()|.  Note that using |line()|
-		would use the current buffer, not the one appending to.
-		Use "$" to append at the end of the buffer.
+		{lnum} is the line number to append below.  Note that using
+		|line()| would use the current buffer, not the one appending
+		to.  Use "$" to append at the end of the buffer.  Other string
+		values are not supported.
 
 		On success 0 is returned, on failure 1 is returned.
 		In |Vim9| script an error is given for an invalid {lnum}.