Re: suggestion on adding arguments to existing functions

[Richard M. Stallman]

    My suggestion is to use `&optional' in a case like this, other things being
    equal (that is, if there is no good reason not to). Why? Because otherwise
    it unnecessarily breaks libraries that use the old form and (more
    importantly, to me) libraries that try to work with multiple versions of
    Emacs. It makes those libraries use ugly constructs such as this (or a macro
    that does the same thing):

That's a good argument for functions that were meant for users to
call, but we need not worry about it for internal functions.  Users
must be prepared for their calling conventions to change.

    [Now, if there were a function that we could use to test the arity, that
    would also be welcome here (a version test is not the first choice, if there
    is an alternative). In Emacs 21 and 22 there is `sub-arity', but that only
    works for built-in functions, IIUC.]

That would be a good feature to add, after the release.
I will add it to etc/TODO, but let's not discuss it now.