WCAG 2.1 – Criterion 1.3.4 – Orientation (Level AA)

Today, we present to you WCAG criterion 1.3.4 (Level AA) regarding orientation.

In simplest terms, content and functions cannot be restricted to displaying in just one orientation – horizontal or vertical. The user must be able to decide how they interact with a given website or application.
The aim of this success criterion is to ensure that developers do not limit the use of a mobile application or website to a specific mode.
Individuals who may potentially have difficulty rotating a mobile device to a horizontal position should not be restricted in accessing content. For example, people who have a phone attached to the handle of an electric wheelchair.

Are there exceptions? Yes.
Content that somewhat forces a particular orientation due to its format.

W3C – World Wide Web Consortium – provides simulations of pianos as an example. Handling the application in a vertical orientation would be ineffective, and the keys might be too small.