What's the function of a function variable's function?

[DrD]

Interestingly, I found nothing in the user guide regarding this usage of a function variable:

CAS enter:
r(t):=[t-sin(t) 1-cos(t)]

Produces:
r:=(t)->BEGIN [t-sin(t),1-cos(t)]; END;
(t)->BEGIN [t-sin(t),1-cos(t)]; END;

Example:
A revolving cycloid at t=0 (rest), position r(0) => [0,0] rotates to pi radians, r(π) => [π,2], completes a full cycle at r(2*π) => [2*π,0].

Is there any further information on this?

-Dale-