OK, but I'd like a callback for the same reason that tick() was implemented.

Basically, ticks of arbitrary type can arrive at different frequencies than real ticks. In other words, this can happen, in this sequence:

tick()
tick()
tick()
generic_tick()
generic_tick()
generic_tick()
generic_tick()
tick()
tick()
tick()
generic_tick()
generic_tick()
generic_tick()
generic_tick()

The idea is to guarantee that all ticks will be caught in all circumstances.