>>> Commutative means that, for functions A:x->x, B:x->x: A(B(x)) == B(A(x)).
> The elusive binary operator here is function composition ;)
I thought you were presenting a general version of the commutative property, not a specialized version for function composition. That explains why I couldn't reconcile your example with other commutative operators (equality, addition, multiplication) without making "x" the operator and "A" and "B", in essence, the parameters.
Writing "(A . B)(x) == (B . A)(x)" or "A . B == B . A" would make the commutative part of the formula a bit more visible--not that it was really hidden. I just wasn't looking at it from the right perspective.