Concurrent Input Mechanisms
Web content does not restrict use of input modalities available on a platform except where the restriction is essential, required to ensure the security of the content, or required to respect user settings.
In plain language
A site shouldn't force people to use only one specific way of interacting (like only touch, or only mouse) — it should let people freely use whichever input method their device supports, even switching between them.
Why it matters
Someone might use a touchscreen laptop with an external keyboard and mouse plugged in, switching between touch, keyboard, and mouse as needed. If a site arbitrarily blocks one of those methods, it removes options people rely on based on their specific abilities and setup.
In practice
Fails this criterion
A web app only responds to touchscreen taps and completely ignores keyboard or external mouse input, even on devices that support both.
Meets this criterion
The same app works seamlessly with touch, keyboard, mouse, or any combination, letting the user switch freely between input methods at any point.
Test it yourself
On a device with more than one way to interact (like a touchscreen laptop), try switching between touch, mouse, and keyboard while using the site. Does everything keep working no matter which input you use?