The intent of this Success Criterion is to ensure that all content is operable from the keyboard. This is the same as Success Criterion 2.1.1, except that no exceptions are allowed. This does not mean that content where the underlying function requires input that depends on the path of the user's movement and not just the endpoints (excluded from the requirements of 2.1.1) must be made keyboard accessible. Rather, it means that content that uses path-dependent input cannot conform to this Success Criterion and therefore cannot meet Guideline 2.1 at Level AAA.
Platforms and user agents usually have conventions for how web content or applications are controlled with a keyboard interface. If content does not follow the platform/user agent conventions it may be difficult to use, as users will need to learn different interaction methods. As a best practice, content should follow the platform/user agent conventions. However, deviating from these conventions does not fail the normative requirement of this Success Criterion.
For instance, buttons that have focus can generally be activated using both the Enter key and the Space bar. If a custom button control in a web application instead only reacts to Enter (or even a completely custom key or key combination), this still satisfies the requirements of this Success Criterion.
This Success Criterion does not require that every visible control that can be activated using a pointer (such as a mouse or touch screen input) must also be focusable and actionable using the keyboard. The normative requirement is only that there must be a way for keyboard interface users to perform the same, or comparable, actions and to operate the content. Generally, the easiest way to achieve this is to provide controls that can be operated with all possible input devices; however, if a web application implements a separate mode of operation for keyboard interface users, it will not fail the Success Criterion.
No additional techniques exist for this Success Criterion. Follow techniques for Success Criterion 2.1.1. If that is not possible because there is a requirement for path-dependent input, then it is not possible to meet this Level AAA Success Criterion.