RE: grep command doc - point out that you can chain now

[Drew Adams]

    I don't think it should be pointed out in the manual because
    you would expect it to work.  However it might be worth mentioning
    it in NEWS, so that users who have tried it in the past know it
    will now work.

I don't think it's obvious ("you would expect it to work"), since Emacs
`grep' is asking for input to the Unix/GNU-Linux `grep' command. Do a `man'
on grep, and you won't see its arguments mentioning this, because piping
output to other commands is not part of the arguments - it is part of the
shell interpretation of Unix/GNU-Linux.

There is nothing (in the prompt, doc string etc.) that would suggest that
you can instead pass it both the args for grep and a chain of piped
commands. I imagine you could pipe anything, not just grep (haven't tried),
and that's certainly not what "you would expect" from a `grep' command
asking for input.

Aside from this consideration, I think this is important enough that it
should be in the doc, not just the NEWS, to bring it to the attention of
users of previous Emacs releases. What's wrong with adding such a "Usage
Note" to the doc?