Accessibility tree
The parallel tree of nodes the user agent maintains alongside the DOM, exposing each element's name, role, state, value, and relationships to platform accessibility APIs and assistive technology.
The accessibility tree is the bridge between the DOM and assistive
technology. Each engine builds and updates it in parallel with the
DOM: a <button> becomes a node with role “button”, a name
computed from its text content, and a focused/disabled/pressed
state synchronised with the DOM. Authors do not interact with the
tree directly; they shape it through HTML elements, ARIA
attributes, and ElementInternals on custom elements. DevTools in
Chromium, WebKit, and Gecko exposes the tree for inspection.