Each Snapshot created has one or more Overlays. The user may add additional Overlays to a Snapshot. Additionally, Snapshots may have multiple users who are allowed to edit that Snapshot; each of these users may have one or more Overlays for the Snapshot. Managing these Overlays is done through the Snapshot Window, which is opened when the user double-clicks on the Snapshot in the Desk Drawer or on the lecture. Figure 2.4.1.4a shows the Snapshot Window opened to a Snapshot with two Overlays.

There are two basic aspects of working with multiple Overlays. The first is the ordering (called the z-order) of the Overlays. This order controls which Overlays are on top of the others. The second tool for managing mutliple Overlays is the Overlay opacities, which allow you to control how much of the background Snapshot is seen as well as how transparent the items on the Overlay are. Combined, these two features give each user the power to define how the Overlays for a Snapshot will be viewed. As mentioned, there are two tools for managing multiple Overlays:

• Ordering Overlays
• Overlay Opacities