For this spot, I use a rounded rectangle maska rounded window if you willthat shows the layers below it. Flash has a quick and easy way to create masks. And with Flash 4 you can mask unlimited layers . Here's how:
To activate the masking effect, all layers (the mask and those masked below it) must be locked, which can be done by clicking the lock icon in the layers (see figure 03:07). I usually wait to do this until much of the animation is complete. I change the mask layer to outline view by clicking on the Outline icon in the mask layer (see figure 03:08). This allows me to see the boundaries of the mask as well as the layers below it.