Commands that modify the text in a buffer can be undone, so that the text reverts to its state before the command was invoked, using Undo . Details of modifying commands are kept in an undo ring so that previous commands can be undone. The undo ring works like a stack, in that commands are pushed onto the ring and can only be popped off on a "last in first out" basis.
Un-Kill can also be used to replace text that has inadvertently been deleted.
Arguments: None
Key sequence: Ctrl+Shift+_
Undoes the last command. If typed repeatedly, the most recent commands in the editing session are successively undone.
The number of items in the undo ring.