In the film Starman, Jenny (Karen Allen) and Starman (Jeff Bridges), an extra-terrestrial who has crash landed on Earth, road trip across the United States in Jenny’s Mustang while evading government agents. Starman offers to drive and explains to Jenny, “I watched you very carefully. Red light stop, green light go, yellow light go very fast.”

Much has been written about web applications, particularly AJAX applications, that ‘break’ the web browser’s back button. There’s more than one type of back button breakage but what is usually discussed in relation to AJAX is the ability (or un-ability) to use the back button to undo the application’s last action.

I think the concern is misguided. The back button is not an undo button.

The back and forward buttons are part of the model of the web as a repository of documents. They allow a user to move back or forward in the chain of visited hypertext nodes, i.e. web pages.

The ‘back as undo’ argument is often supported by a usability study that shows mere mortal users depend on using the back button as an undo. I think that’s a little bit like using a study that shows automobile drivers speed up on a yellow light to argue for swapping the meanings of green and yellow traffic signals.

I don’t think browser back button behavior is quite as important as road safety but I do think there is an impedance mismatch between the web browser as hypertext document platform and the web browser as application platform.

‘Undo’ is an application action. The back button doesn’t undo anything. It loads a previous page. Spackling over the difference is a bad idea.

Link: Hypertext and Application Workflow (or The Case for Single Node Apps).