|2.5.1 Pointer Gestures|
All functionality that uses multipoint or path-based gestures for operation can be operated with a single pointer without a path-based gesture, unless a multipoint or path-based gesture is essential.
SC 2.5.1 -Pointer Gestures states that all operations must use simple gestures that need only a single touch. Gestures that need two fingers or complicated movements can be hard to operate for people with hand tremors or limited movement. Users with alternative input devices such as a mouth stick, sip-and-puff, or head mouse also benefit. Simple gestures are easier for someone with cognitive impairments to remember and use. If the site or application does use multi-touch gestures, be sure to also provide simple interfaces.
Who it helps:
This requirement applies to web content that interprets pointer actions (i.e. this does not apply to actions that are required to operate the user agent or assistive technology).
The dragging of a slider requires a precise path of the user's pointer movement to control the volume
Buttons are added as an alternative way for users to adjust the volume with simple clicks.