On 2016-11-04 Fri 14:31 GMT-0700, Eli Zaretskii <eliz@gnu.org> wrote:

> Do we really need to tell people that an omitted argument defaults to
> nil?  And if we do, why in this section?

Hmm, I didn't notice that we don't say optional args are default to nil
in the doc. Never mind, we should close this bug.

Despite that, I sort of see some confusion in the doc when mentioning
optional args: Sometimes we say "omitted or nil" (e.g.,
face-all-attributes FRAME arg), sometimes we just say "nil" (e.g.,
face-attribute FRAME arg). Perhaps more consistency is less confusing.