-LY_DEFINE (ly_option_usage, "ly:option-usage", 0, 0, 0, (),
- "Print @code{ly:set-option} usage.")
+LY_DEFINE (ly_option_usage, "ly:option-usage", 0, 1, 0, (SCM port),
+ "Print @code{ly:set-option} usage. Optional @var{port} argument"
+ "for the destination defaults to current output port.")