It's great when you can undo after you have already saved a document and go back, back, back... It would be even greater if everything could be really undoable. Take for example Adobe(R) Acrobat(R) Reader 9.0.0. I was reading a book of 1200 pages. I was reading one of the internal pages (don't remember which) and had arrived to the bottom of the window. I moved my hand to press the key "Page Down", but I pressed the wrong (nearby) key, which happens to be the "End" key. Ok, I said, there's the Undo command. No way, said Acrobat Reader, you can't undo. The rationale is probably: "The user has not edited the document, there is nothing to undo". Why not adopting the rationale: "Every time a key is pressed, chances are it was a mistake"???
Dear reader, don't think that, just because today's software allow for unlimited undoing, you can really undo everything. Actually there are a lot of important and common things that can't be undone, or can be remedied to, but only using a command different from Undo. Try for example to click a link in this page and to return here with an Undo. Does it work? Try typing a long sentence with your word processor and to remove the last word only with Undo. What happens?
Luckily, everybody knows how to jump back to the previous page with the command go back and to delete the last word by selecting it and cutting it away. How do you find the page you were reading with Acrobat?
Adobe Reader takes 172.6 MB on my hard disk. It's larger than many historical operative systems (combined). It's also much larger than my first hard disc (40 MB), yet it can't undo. It's really a mystery what's hidden inside. There is potential room for a million of viruses.
I have an assignment for you. I mean you guys who haven't the least idea of what NMR means but nonetheless try to post comments into my blog only to link to your web sites. I have always deleted your posts. This time I want to give you a chance.
Read the credits of Adobe Reader (they appear after you open the "about" box). If you can write the exact number of people who appear into the credits, I will not delete your comment.