A lot of programs have some kind of auto-save, here is how it works in Microsoft Word. While editing your document, it is auto-saved, but as a new, hidden file. When you manually Save, this new file overwrites the old, and a Save As does the same, but with the new name, not wiping the old document. You can argue that this is messy, and only a hack to get around the paradigm. It all depends on how people want to work, giving the program the responsibility to handle it.