I think those constraints are often the same as when you create a new record, so you can reuse code from there. But I'm sure there can be edge cases that make

I think those constraints are often the same as when you create a new record, so you can reuse code from there. But I'm sure there can be edge cases that make it tricky for some apps and/or situations. Undo and redo aren't important features for every web app - in some they would't make sense at all - but for applications that facilitate any kind of creative process, such as photo editing, 3d modeling, or drawing, they are very important features to include. Users often want to try out an idea, then go back to an earlier version if the idea doesn't work out. In most cases for apps like these implementing undo/redo gives you a ton of usability bang for your proverbial buck.