The intent of this Success Criterion is to ensure that, wherever possible, content can be operated through a keyboard or keyboard interface (so an alternate keyboard can be used). When content can be operated through a keyboard or alternate keyboard, it is operable by people with no vision (who cannot use devices such as mice that require eye-hand coordination) as well as by people who must use alternate keyboards or input devices that act as keyboard emulators. Keyboard emulators include speech input software, sip-and-puff software, on-screen keyboards, scanning software and a variety of assistive technologies and alternate keyboards. Individuals with low vision also may have trouble tracking a pointer and find the use of software much easier (or only possible) if they can control it from the keyboard.
Examples of "specific timings for individual keystrokes" include situations where a user would be required to repeat or execute multiple keystrokes within a short period of time or where a key must be held down for an extended period before the keystroke is registered.
The phrase "except where the underlying function requires input that depends on the path of the user's movement and not just the endpoints" is included to separate those things that cannot reasonably be controlled from a keyboard.
Most actions carried out by a pointing device can also be done from the keyboard (for example, clicking, selecting, moving, sizing). However, there is a small class of input that is done with a pointing device that cannot be done from the keyboard in any known fashion without requiring an inordinate number of keystrokes. Free hand drawing, or watercolor painting require path dependent input. Drawing straight lines, regular geometric shapes, re-sizing windows and dragging objects to a location (when the path to that location is not relevant) do not require path dependent input.
The use of MouseKeys would not satisfy this Success Criterion because it is not a keyboard equivalent to the application; it is a mouse equivalent (i.e., it looks like a mouse to the application).
It is assumed that the design of user input features takes into account that operating system keyboard accessibility features may be in use. For example, modifier key locking may be turned on. Content continues to function in such an environment, not sending events that would collide with the modifier key lock to produce unexpected results.
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 mouse or touch screen 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.
Ensuring keyboard control by using one of the following techniques.
Providing keyboard-controllable event handlers using one of the following techniques: