Dock slices are a new way to get quick, glanceable information when you need it using Unite 4. To enable dock slices, go to File→ Start Dock Monitor. This will bring up a selection tool that allows you to select any part of the active site. Whatever you select will temporarily replace the dock icon with a live feed of this selection.
Once you activate the dock monitor, you can click and drag on the active window to select which portion to display in the dock. Once you are finished, click outside of the boundary, and you can continue to work within your app with the monitor activated.
You can edit or stop Dock slices at any time by going to the File menu.