2.1 Keyboard Accessible (Level AAA)
Success Criterion 2.1.3 Keyboard (No Exception)
All functionality of the content is operable through a keyboard interface without requiring specific timings for individual keystrokes.
Keyboard (No Exception) Explained
This is a more stringent version of SC 2.1.1 that states that everything, without exception, must be keyboard accessible.
A web page that has, for example, an embedded helicopter simulator that cannot be piloted without a mouse may conform at Level A. However, if the developers of the simulation devise a way to pilot the helicopter using the arrow keys, the space bar, the Enter key, and the Shift key, then the site may conform at Level AAA.