diff --git a/runtime/doc/channel.txt b/runtime/doc/channel.txt
index fbe4d3f..111a56d 100644
--- a/runtime/doc/channel.txt
+++ b/runtime/doc/channel.txt
@@ -618,6 +618,9 @@
 ch_log({msg} [, {handle}])					*ch_log()*
 		Write String {msg} in the channel log file, if it was opened
 		with |ch_logfile()|.
+		The text "ch_log():" is prepended to the message to make clear
+		it came from this function call and make it easier to find in
+		the log file.
 		When {handle} is passed the channel number is used for the
 		message.
 		{handle} can be a Channel or a Job that has a Channel.  The