The `help` command displays on-line help. To specify information on a
particular topic use the syntax:
help {<topic>}
If <topic> is not specified, a short message is printed about `gnuplot`
(Note:gnuplot ). After help for the requested topic is given, a menu of
subtopics is given; help for a subtopic may be requested by typing its name,
extending the help request. After that subtopic has been printed, the request
may be extended again or you may go back one level to the previous
topic. Eventually, the `gnuplot` command line will return.
If a question mark (?) is given as the topic, the list of topics currently
available is printed on the screen.