The Undo selection works when editing a script, sketch, item, and so on. If our fickle fingers (at least mine are when typing fast) fly furiously into a typo or an action not intended, just click on the Edit menu's Undo selection and the last action performed will be erased. Better yet, use the shortcut for Undo, Ctrl+Z. This shortcut works in many other programs also, such as Microsoft's Word word processing software in which I am writing this book. Not that I ever make misteaks... er... mistakes.