Prysm supports masks in the following manner.
- A mask layer can contain multiple frame spans.
- Each frame span can contain only shapes or a movie clip. In the case of a movie clip, the movie clip can have 1 frame span with shapes only.
- Drawing objects and shape primitives are supported.
- Motion tween and Classic tween are supported in mask layers.
- The frame count of the mask layer frame span affects the duration of other animations on the stage.
- If the mask layer has the most frames in the current timeline, all other animations in the timeline will have a longer duration.
- Strokes are counted in the HTML mask and ignored in Animate.
- All shapes and drawing objects in the mask layer are counted towards the mask.
- Masks respect the animation iteration count selected for a play, gotoAndPlay and playFromTo actions while other animations don't.
- Components don't work with masks.
- Masks can be slightly offset from other motion tween animations, because currently mask tweens aren't interpolated.
- Using playFromTo stops animations at the end of the frame, so other tweened elements will be ahead in their animation compared to masks.
- When playFromTo is used, mask tweens will sometimes flicker at the last frame.