Multiple animation running at the same time altering the same variable:
- in a real world applications, very often more more than one timeline can animate the same variable and as the timelines are typically triggered by user events, very often they run at the same time, thus the same variable is being animated from several timelines at the same time.

We need a solution which will clearly describe what is going to happen with the variable in such a cases. The most typical cases are:
- the animation started later has a priority over the old one,
- if the animation is running, the other animation does not do anything
- both animations are run at the same time and their values are summed up

Also think what happens when an animation is modifying an variable and user decides to overwrite the variable from a custom code. How this should work (again we need to think about additive or replace behavior).