help [-c class]
Not really a online help, but displays a help screen showing you all the
key bindings. The first pages list all the internal commands followed by
their current bindings. Subsequent pages will display the custom
commands, one command per key. Press space when you’re done reading each
page, or return to exit early. All other characters are ignored. If the
-c option is given, display all bound commands for the specified
command class. See also Default Key Bindings section.