bug#50658: Error messages including function names violates coding conventions

[Stefan Kangas <stefan@marxist.se>]

Eli Zaretskii <eliz@gnu.org> writes:

>>    • An error message should start with a capital letter but should not
>>      end with a period.
>>
>> These cases are all flagged by checkdoc when it tries to enforce the
>> above convention.
>
> I think it's a bug in checkdoc: the error message text, which excludes
> the function name, fulfills the requirement.

While working on this, I realized that it is impossible to know if in
something like:

    (error "frobnicator not available")

The 'frobnicator' part is a Lisp symbol (that can be in lower-case), or
if it is a regular word (that must be capitalized).  It would obviously
be helpful if our conventions could be unambiguous.

Perhaps we could add a requirement here, something like: a Lisp symbol
must always be in `quotes', or behind ": "?

(I guess this would also affect the text we want to put in `(elisp)
Documentation Tips'.)