-It exports a single function: B<off>(I<url>, [I<argument> => value...]).
-This function that returns a list of download links,
-as returned by the service.
+The module exports (on request) a single function, B<off>(I<url>,
+[I<parameter> => value, ...]). It takes a URL and an optional list of
+parameters (key/value pairs). It returns a list of download links. An
+empty list is returned if the Offliberty service returns no URLs (for
+example if Offliberty encounters an error or the URL is invalid). Dies
+if unable to contact Offliberty (for example if there is no internet
+connection or a firewall blocks the connection).
+
+The supported services and parameters are undocumented. From empirical
+testing, when requesting a YouTube URL the service will return an
+audio-only URL when called with no parameters, and two URLs
+(audio-only and audio/video) when called with the parameter
+B<video_file> set to B<1>. In contrast, Vimeo URLs with no parameters
+return both audio-only and audio/video variants.