This page deals with criterion 1.3.4 and is all about orientation. The criterion states:

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.

I rarely see any problems relating to this criterion. What I do see is misunderstandings about it. This criterion is not about how the content displays. It is only about whether or not a user has choice over which orientation they use.

The important thing here is not to restrict orientation. My question is, why would you? It is not that easy to do and there aren't many reasons you would want to. We will look at a few exceptions to that at the end.

What is orientation?

I find it easiest to think about orientation with a piece of paper. Take a piece of paper. It has to be a rectangle, not a square. Hold the piece of paper with the shortest edge at the top. That is portrait. Turn it round so the longest edge is at the top. That is landscape.

Mobile phone in portrait orientation
Portrait orientation
Mobile phone in landscape orientation
Landscape orientation

I enjoy a bit of amateur photography. I would describe myself as a landscape photographer. I love capturing scenery! Landscape photography is best when the photo is in landscape orientation, whereas a portrait of a person might be better in portrait orientation because people tend to be taller than they are wide.

What is an essential orientation?

There are some things that, by their nature, only really work in either portrait or landscape. That is often because of the design of something else, that is not digital. Examples might be:

Testing for 1.3.4 Orientation

The only real test is: can you view the content in either orientation? In other words, has the orientation been locked? At this stage, forget about whether it looks good or not. That will come later.

If you use the Web Developer toolkit or Mobile Simulator extension, you can view content in different orientations there, just to check. However, you shouldn't need to check as you would know if you'd spent time locking the orientation.