animation timing
animation is tested with an event value with positive and negative and without offset for begin
and a duration of 2s or 4s. The event is a click or an activation of the small circles above.
Referenced is a simple document with a blue stroked square.
From left to right without offset, with positive and with negative offset.
For comparison a slightly larger gray rectangle with an animation
for fill is provided behind the animation. The animations are visible the same times as
these rectangles are visible as gray borders around it.