animation timing
animation is tested as an end syncbase for set animations syncbase values with
positive and negative and without offset for begin and a duration of 2s.
Referenced is a simple document with a blue stroked square.
From left to right without offset, with positive and with negative offset.
For comparison another syncbase is derived from a slightly larger gray rectangle.
The circles on top of the animation element have the begin with the related syncbase value.
The animations are visible the same times as these rectangles are visible as gray borders around it.
And the circles on top appear always as adjacent pairs, the circle dependent on the animation in
blue, the other in blue gray.