bug#46910: 27.1; (elisp) RX doc

[Drew Adams]

1. `Rx Constructs' doesn't explain that the "constructs" are used in
arguments to macro `rx'.

E.g.: "some-string" is not an RX expression.
      (rx "some-string") is an RX expression.

Please make this clear.

2. `Rx Constructs': Don't show things like `\sCODE' without saying what
CODE means.  If the column title for the table explaining RX names is
`Syntax character' or `Category character' then that's apparently what
CODE corresponds to for `\sCODE' or `\cCODE'.  But there's no way to
know that unless you're already familiar with `\s' and `\c' syntax.

3. `Rx Constructs', `Zero-width assertions': Call this `Zero-width
matching' or some such.

4. `Rx Functions': RX-EXPR is used as parameter name for what is, I
guess an Rx construct (the language used in `Rx Construct').  Expression
or construct?  Make it clear that RX-EXPR is an RX construct, if that's
what it is.  And consider adding an xref to `Rx Construct'.

5. `Rx Functions': A couple places talk about `'regexp' forms', but
those are specified nowhere, AFAICT.  The same places talk about
'literal' forms, which are specified, but which don't seem to work (?).
(See bug #46909.)


In GNU Emacs 27.1 (build 1, x86_64-w64-mingw32)
 of 2020-08-12
Repository revision: 86d8d76aa36037184db0b2897c434cdaab1a9ae8
Windowing system distributor `Microsoft Corp.', version 10.0.19041
Configured using:
 `configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static''