It's built in in - at least in bash ;)
Not only that, but (correct me if I'm wrong - that's why I'm
posting this) it appears that the docs for some things are
split into docs that appear in HTML in /usr/share/docs, and
docs that appear via the "help" command (the data for which
is stored somewhere where I haven't found it yet, although
I haven't really looked...).
Additionally, in some cases it appears that there may be information
available via the "help" docs which is not in the HTML docs,
and vice versa.
I recently engaged with "exim", and if it weren't for the fact that
I found an obscure reference buried in the back yard in the dead of
night, to the fact that there is an "exim-docs" package which needed
to be loaded *in addition* to the exim docs which turn up in the
"/usr/share/docs" directory, I would never have known it was there
- and that package seems to be what turns up via the "help" command.
If the "help" command is only available in "bash", I'll have to
do some negotiating... I'm a csh/tcsh nazi and hate anything that
looks like the original Bourne shell on general principles (or no
principles at all, FTM)
Please correct me if I'm wrong about any of this, since this is one
area I've been meaning to explore and haven't Gotten Around To It