In Atlantis you can undo any operation performed on your document: typing, deleting text, formatting etc.
So if you have accidentally made an undesirable change to your document, you can easily undo this change.

To undo the most recent operation, click the Undo toolbar button, or choose the Edit | Undo menu command, or press CtrlZ or AltBackspace. You can undo as many operations as you need.

To undo all the operations performed on the active document, click the Undo all toolbar button.

Every undone operation can be redone. To redo the last undone operation, click the Redo toolbar button, or choose the Edit | Redo menu command, or press CtrlY or CtrlShiftZ or AltShiftBackspace.
You can redo as many recently undone operations as you need.

You can also quickly redo all the undone operations. For this click the Redo all toolbar button.