Tasks and Expressions
The Task window allows you to create multiple auxiliary timelines, and to specify their triggering conditions using expressions. Auxiliary timelines behave very much like the main timeline, but can be started and stopped independently.
If an auxiliary timeline displays images on stage, those images will appear on top of any images originating from the main timeline. You can control the order in which images from multiple, concurrent auxiliary timelines interact by dragging the tasks to the desired order in the Task window.