Re: emacs-26 b90e91c: Fix last change of @key markup

[Eli Zaretskii <eliz@gnu.org>]

> From: Michael Albinus <michael.albinus@gmx.de>
> Cc: Eli Zaretskii <eliz@gnu.org>
> Date: Thu, 01 Feb 2018 19:48:24 +0100
> 
> for future changes I might apply, could you pls tell me what was wrong
> with my changes?

@key is only for names of keys, not for names of characters or
commands.  Your changes to add @key were mostly good, but they went a
notch too far, in that they included _any_ instance of "TAB" or "RET"
or "SPC", including, for example, this:

  @item big-indent
  @vindex whitespace-big-indent-regexp
  Highlight too-deep indentation.  By default any sequence of at least 4
  consecutive TAB characters or 32 consecutive SPC characters is
  highlighted.  To change that, customize the regular expression

Here, TAB and SPC refer to characters, not keys.

If that still doesn't make the criterion clear, consider this: the
purpose of @key is to avoid the erroneous interpretation of "RET" to
mean literal 3 characters R E T.  And such an erroneous interpretation
can only happen in the context of describing keyboard input or keys
the user presses, it cannot happen when the text refers to characters,
as in the above excerpt.  (Another way of looking at this is to see
how TeX renders @key: the result looks like a key on a keyboard, and
that is, of course, inappropriate when talking about anything other
than a keyboard key.)

HTH