[O] completing-read question

[42 147]

Hey everyone,

My init stabilized about a year ago and therefore I've actually been
spending more time working in org-mode than customizing it!

But that comes at a cost. My Emacs Lisp has become quite rusty. Recently I
started customizing again, and I wanted to use the completing-read function
-- but I am curious what the numbers in these lists are used for.

This is an example I found in one of the tutorials online:

(completing-read
 "Complete a foo: "
 '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))
 nil t "fo")

This function appears to work fine without the 1, 2, 3, 4.

If this is outside the scope of this particular mailing list, I will gladly
be directed elsewhere.