The intent of this Success Criterion is to ensure that content displays in the orientation (portrait or landscape) preferred by the user. Some websites and applications automatically set and restrict the screen to a particular display orientation and expect that users will respond by rotating their device to match, but this can create problems. Some users have their devices mounted in a fixed orientation (e.g. on the arm of a power wheelchair). Therefore, websites and applications need to support both orientations by not restricting the orientation. Changes in content or functionality due to the size of display are not covered by this criteria which is focused on restrictions of orientation.
Historically, devices tended to have a fixed-orientation display, and all content was created to match that display orientation. Today, most handhelds and many other devices (e.g., monitors) have a hardware-level ability to dynamically adjust default display orientation based on sensor information. The goal of this Success Criterion is that authors should never restrict content's orientation, thus ensuring that it always match the device display orientation.
It is important to distinguish between an author's responsibility not to restrict content to a specific orientation, and device-specific settings governing the locking of display orientation.
Many hand-held devices offer a mechanical switch or a system setting (or both) to allow the user to lock the device display to a specific orientation. Where a user decides to lock their entire device to an orientation, all applications are expected to pick up that setting and to display content accordingly.
This Success Criterion complements device "lock orientation" settings. A web page that does not restrict its display orientation will always support the system-level orientation setting, since the system setting is picked up by the user agent. Alternatively, where a device-level orientation lock is not in place, the user agent should display the page according to the orientation of the device (either its default, or the current orientation determined by any device senors).