bug#22748: 24.5; (elisp) `Type Predicates': Repeat the rule from `Coding Conventions'

[Drew Adams <drew.adams@oracle.com>]

> "Coding Conventions" are about future code;

No, they describe the conventions that we follow.
That's general: past, present, future.

> "Type Predicates" describe the reality.  These two are not
> necessarily identical.

Agreed.  But `Type Predicates' specifically points to the
convention.  It should link to it, so readers can understand
just what that _convention_ is - as opposed to the more lax
description of "the reality".

FWIW: I was pretty sure that this convention was described
somewhere, so I tried `i predicate' and then narrowed that
to "type predicates" and landed at `Type Predicates'.

I did not find what I was looking for there, wrt the rule
for naming type predicates.  I then resorted to, yes,
searching the manual (I even searched the Emacs manual, as
well), using regexps such as "[^CM]-p\b"...  Eventually, I
got to (elisp) `Coding Conventions'.

Sure, I should have started there, perhaps.  But I should
have also been able to get there easily from `Type Predicates'
after using `i predicate'.  Just one user, sure.

Why you would not want to add a cross-reference to the
node that actually defines the "general Lisp convention for
predicate functions" is beyond me.  Perhaps you are having
a bad day?  If you don't have time to add that cross-ref
now, why not leave the bug open until someone does?

Why should this node mention, vaguely, "a general Lisp
convention for predicate functions" without helping users
find out what that convention is?

> Closing.

Too bad.