This attribute controls which one of a Mapping's two possible
coordinate transformations is considered the "forward"
transformation (the other being the "inverse"
transformation). If the attribute value is zero (the default),
the Mapping's behaviour will be the same as when it was first
created. However, if it is non-zero, its two transformations
will be inter-changed, so that the Mapping displays the inverse
of its original behaviour.
Inverting the boolean sense of the Invert attribute will cause
the values of a Mapping's Nin and Nout attributes to be
interchanged. The values of its TranForward and TranInverse
attributes will also be interchanged. This operation may be
performed with the astInvert function.