Ie:

array(string) lesser()    - gives back a list of possible xxx's.
object xxxs()             - gives back a list of possible n's.
object xxx(mixed n)       - gives back xxx n
object xxx(object(Xxx) o) - gives back the corresponing xxx

The list of n's (as returned from xxxs) are always in order.

There are two n's with special meaning, 0 and -1. 0 always gives the first xxx, equal to my_obj->xxx(my_obj->xxxs()[0]), and -1 gives the last, equal to my_obj->xxx(my_obj->xxxs()[-1]).

To get all xxxs in the object, do something like Array.map(my_obj->xxxs(),my_obj->xxx).

xxx(object) may return zero, if there was no correspondning xxx.