Use the Edit menu Undo command to undo your previous editor pane actions. You can undo the previous 256 editor operations, if required.
You can undo the following types of action.
Last single keystroke
Cut
Paste
This command is disabled when a command cannot be undone; that is, you have not previously performed an action in the editor pane that can be undone.
To undo your last action, perform one of the following actions
Select the Undo command from the Edit menu
Press Ctrl+Z
Press Alt+Backspace
Your previous action is then undone. Repeat this action to undo up to 256 previous actions, if required.