WCAG2.1 Success Criteria (SC) 1.3.4 Orientation, is intended to enable people to view content in the orientation (portrait or landscape) that they prefer. Here is the SC itself:
1.3.4 Orientation (Level AA): Content does not restrict its view and operation to a single display orientation, such as portrait or landscape, unless a specific display orientation is essential.
It used to be the case that content was created to be viewed on fixed orientation devices, like desktop monitors. These days, content is viewed on phones, tablets, hybrid laptops, and even desktop monitors, all with the capability to rotate between portrait and landscape orientations.
SC 1.3.4 prevents content from being tied to a particular orientation, because imposing an orientation on someone can make the content unusable. Think of someone who has mobility difficulties, and who has their tablet mounted on their wheelchair in a fixed position they cannot adjust; or a person with low vision who uses high magnification to enlarge the size of content, and who prefers to use a landscape orientation because it means more content can be viewed comfortably.
This is the definition of “essential” in WCAG2.1:
Essential: if removed, would fundamentally change the information or functionality of the content, and information and functionality cannot be achieved in another way that would conform.
SC 1.3.4 includes a bank cheque, a piano application, slides for a projector, and VR content (where portrait and landscape may be meaningless) as examples where orientation might be considered essential.
It is worth mentioning that this SC is only applicable to web content, it doesn’t apply to device specific settings that someone may use to restrict their device to a particular orientation. In other words, authors should create content that automatically adapts to the orientation of the device it is being viewed on.
