Mixere allows you to take snapshots of a document. A snapshot is a recording of the state of every track in a document, at a particular moment. A snapshot can be restored, which means the tracks revert to the state they were in when the snapshot was taken. A document can contain any number of snapshots, and the snapshots are saved as part of the document. Snapshots can be assigned shortcut keys, which allow them to be restored quickly, facilitating rapid transitions.
See also Taking a snapshot, and Restoring a Snapshot.