Undoes the last editing operation.
procedure Undo;
(Introduced in version 1.3)
This method does nothing if there is no action to undo.
Information about the operation to redo is returned by the methods UndoAction and UndoName.
This method must be called only when the document is formatted.
This method is called when the user presses Ctrl + Z ( Command + Z on macOS) or Alt + Backspace .
Method type: 
editing-style.
See also:
▪Redo;