bug#46627: [External] : bug#46627: [PATCH] Add new help command 'describe-command'

[Drew Adams]

> > There seems to be little difference between the proposed
> > describe-command command and the existing describe-function command.
> > Whatever the former could do, the latter already does.

Yes, the latter can do more.  Just as `integerp' can do
more than `natnump'.  Just as `eval-buffer' can do more
than `eval-region'.

> The main difference is in the completion these commands
> offer.  describe-command completes only on commands.

Yes, that's an important difference.  In addition,
_only commands are accepted_ as input, regardless
of whether you use completion.

(At least that's what my implementation does.
`completing-read' uses `commandp' as PREDICATE and
`t' as REQUIRE-MATCH.)