Provide simple controls for complex gestures
A path-based gesture asks the reader to move a finger along a route, and plenty of people cannot. G215 adds single-pointer controls that do the same job, sitting over or next to the content. W3C's description and test are narrower than the title suggests, written around content sliders, where the check is that controls exist to advance to the adjacent chunk of content. The rule underneath is broader. 2.5.1 Pointer Gestures, at Level A, covers pinch-to-zoom on a map and two-finger rotation as well, and still requires a single-pointer alternative, so the advice holds even where the technique's own example does not. W3C attaches a warning here too. Author-supplied path-based and multipoint gestures usually stop working when a screen reader is running, because assistive technology consumes them first.
How we find it in an audit
Our reviewers try to operate every gesture-driven component with single taps and clicks only. Maps, carousels, sliders, image comparisons, signature pads. Where a gesture is the only route, that is a finding. Then we repeat the pass with a screen reader running, because gestures that worked a moment ago often stop.
How affected users experience it
A head pointer produces one contact point and no path. So does a mouth stick, a single switch, and a shaking hand. For all of them a map that zooms only by pinch is a map locked at whatever view it loaded with. Adding plus and minus buttons costs a few lines and does not take the gesture away from anybody who prefers it.
Passes vs. fails
Passes
The map adds visible plus and minus buttons, arrow pan controls and double-tap to zoom, and the gestures remain for those who can use them.
Fails
An embedded map that zooms only by pinching and pans only by dragging, so a head-pointer user is stuck at the default view forever.
Other ways to satisfy this rule
3 guides on this site are filed under 2.5.1 Pointer Gestures. W3C lists this one as sufficient for that rule on its own. Implement it correctly, in a way your readers' software actually supports, and the rule is met.
This guide is our interpretation of W3C technique G215: Providing controls to achieve the same result as path based or multipoint gestures. W3C publishes its techniques as guidance rather than as the standard, and says so on every one of them. The success criterion is what conformance is measured against, and a technique is one documented way to meet it.