When the History » Purge… command is executed, the following window appears:
You may select the way you want to purge a history.
Purge redo tail - all phantom operations (or operation tail) are dropped and removed.
Purge branches - all branches except the current one are dropped and removed.
Clear history - all operations in a history are deleted. The document state is NOT changed, all modifications are “merged” into the single operation, which becomes an operation list root.
Purge all - remove all operations except the very first one. In most cases (if Clear History command was not used), this root operation is “Open” or “New”.