As a designer I want to be able to design an animation between two UI states once and then use that animation for both state change direction. This means that the editor should support creating these type of animations.

Some ideas how this could be done:

• Allow artist to create a "slide clip" or "referenced slide" that only refers to another slides content and modifies the playback in some way (e.g. slow down to 50%, reverse direction etc.). This is similar to how digital audio workstations abstract an actual audio file on the disk as audio clip that you see in the editing timeline. One audio file can be referenced by multiple audio clips in the editor and different clips can refer to different time stamps of the file and have different directions for playback.
• Add to slide properties an option to play a slide in reverse.
• Allow doing this with duplicate slide and then have Edit-Reverse Timeline function.