chart:interpolation

Greetings!

http://tools.oasis-open.org/issues/browse/OFFICE-3662

raises the issue of adding these four values to:

step-start
step-end
step-center-x
step-center-y

to chart:interpolation.

In passing it is mentioned that some applications have other values.

Two questions:

1) Anyone (Andreas?) care to venture the definitions for these steps.