[css3-transitions] Complex easing functions

Hi,

After reading though the current transitions draft, I am wondering about
support for more advanced easing functions, with more complex curves and
values that fall outside the range [0, 1]. Such functions are required for
'elastic' or 'bounce' transitions, which are a popular way of providing more
natural easing, particularly for movement, but do not seem possible with the
current proposal. There is a useful easing functions visualiser here that
provides samples for each type:
http://www.robertpenner.com/easing/easing_demo.html

This sort of easing is possible using JavaScript libraries, such as Mootools
or jQuery with the easing plugin, and it be a shame if the transitions
module were not to include an equivalent degree of capability. Is there a
reason why the proposal could not be modified to allow multiple bezier
curvers within a timing function, and allow values to fall outside the range
[0, 1], so long as the final values ended at 0,0 or 1,1?

Thanks,
Jon Rimmer