Usability Standard 3:
Keep the User in Control

Users often choose system functions by mistake and will need a clearly marked "emergency exit" to leave the unwanted state without having to go through an extended dialogue. Support undo and redo.10

In sequential processes like e-commerce transactions or long forms, let users to undo an error without undoing all their work. Everyone has encountered a site that erases everything the user has entered in a form if s/he makes a single error.

If a user accidentally chooses the wrong destination in a site, s/he will probably use the browser's "back" button to return to the original page. If the site uses frames or generates dynamic pages on the fly, this may not work. If this is the case, provide clearly marked links to return the user to the original state.

While a user may accidentally choose an unwanted link or action, a site should never make unwanted demands on a user. For instance, many sites force a particular browser version or screen resolution on the user. In the case of many intranets, the client knows what browser and resolution the users will employ. With most Web sites, this is not known.

Prepare the site to degrade gracefully, i.e. to display properly even if the user employs an older browser version, turns off graphics, or can't use all the bells and whistles like Shockwave. This becomes more important as cell phones and personal digital assistants begin to include crude browsers that resemble Mosaic more than IE 5.5.

Other sites force the user to surrender personal data -- name, e-mail address, job title, location, and so forth -- before allowing access to even basic information. In such cases, most users will leave the site or provide false information. Demonstrate the value of the site to the user, disclose exactly how personal data will be used, and then request a minimal amount of personal data -- just enough to provide the user with a service.

^{Mosaic: A text-only browser used in the late Jurassic, i.e. 1993.}