Making group masks

A group mask creates a mask shape from the top object of a group. Any area of the other grouped objects that is covered by the top object becomes visible when the mask is applied; all other areas of the group become invisible. You can use this effect in an animation, for example, to make it look as though objects are moving under or behind the background.

Note: A mask object that will not export as vectors to SWF will use its bounding box as the mask shape.

To create a group mask:

1. Select the objects you want to group. Make sure that the object you want to use as a mask is at the top of the group's stacking order.
2. Choose Object > Group.
3. Choose Object > Top Object Is Mask.

Grouped objects, and with the top object as the group mask