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Can I Use Accessibility Object Model (AOM)

Track the implementation status of the AOM in various browsers.

Summary

Last updated: April 15, 2022

Chrome Safari Firefox
Phase 1: Reflect simple ARIA attributes on DOM nodes. Yes Yes Yes
Phase 2: Reflect element references for IDREF attributes No No No
Phase 2: Synthesized keyboard events aka User action events from Assistive Technology No Yes No
Phase 2: Custom element semantics on ElementInternals Yes No No
Phase 2: New accessibilty-specific InputEvent types Abandoned Abandoned Abandoned
Phase 3: Build virtual accessible nodes. Blocked Blocked Blocked
Phase 4: Query computed accessibility tree/properties. Partial Partial Partial

Phase 1: Reflect simple ARIA attributes on DOM nodes.

element.role = "button";
element.ariaLabel = "Click Me";

Phase 2: Reflect element references for IDREF attributes

*Not yet implemented. Primarily intended to support Accessibilty refs across shadow root boundaries. *

Spec: https://whatpr.org/html/3917/common-dom-interfaces.html#reflecting-content-attributes-in-idl-attributes:element

element.ariaActiveDescendantElement = otherElement;
element.ariaLabelledByElements = [ anotherElement, someOtherElement ];

Phase 2: Synthesized keyboard events aka User action events from Assistive Technology

UAs synthesize logical keyboard equivalents for related AT actions.

Examples: AT increment/decrement on a slider will send synthesized up/down arrows. Dismiss on a dialog will send synthesized Escape key.

More detail: https://github.com/WICG/aom/blob/gh-pages/explainer.md#user-action-events-from-assistive-technology

  • Safari/WebKit (supported)
  • Chrome/Chromium (unsupported)
  • Firefox/Gecko (unsupported)
customSlider.addEventListener('keydown', (event) => {
  switch (event.code) {
  case "ArrowUp":
    customSlider.value += 1;
    return;
  case "ArrowDown":
    customSlider.value -= 1;
    return;
});

Phase 2: InputEvent types

(Abandoned path. No near-term planned support for Accessibilty-specific events.)

Phase 2: Custom element semantics on ElementInternals

Currently being implemented in Chrome: https://chromestatus.com/feature/5962105603751936

Spec: https://whatpr.org/html/4658/custom-elements.html#native-accessibility-semantics-map

class CustomTab extends HTMLElement {
  constructor() {
    super();
    this._internals = customElements.createInternals(this);
    this._internals.role = "tab";
  }

  // Observe the custom "active" attribute.
  static get observedAttributes() { return ["active"]; }

  connectedCallback() {
    this._tablist = this.parentElement;
  }

  setTabPanel(tabpanel) {
    if (tabpanel.localName !== "custom-tabpanel" || tabPanel.id === "")
      return;  // fail silently

    this._tabpanel = tabpanel;
    tabpanel.setTab(this);
    this._internals.ariaControls = tabPanel;    // does not reflect
  }

  // ... setters/getters for custom properties which reflect to attributes

  attributeChangedCallback(name, oldValue, newValue) {
    switch(name) {
      case "active":
        let active = (newValue != null);
        this._tabpanel.shown = active;

        // When the custom "active" attribute changes,
        // keep the accessible "selected" state in sync.
        this._internals.ariaSelected = (newValue !== null);

        if (selected)
          this._tablist.setSelectedTab(this);  // ensure no other tab has "active" set
        break;
    }
  }
}

Phase 3: Build virtual accessible nodes.

Blocked by w3ctag/design-principles#293

Phase 4: Query computed accessibility tree/properties.

Partial testing context in WebDriver (computedRole/computedLabel) is already shipping in all implementations.

Investigation into additional follow-on WebDriver interfaces for accessibilty.

Full Tree Access

Interop investigation into test-only interface for Accessibilty Tree Dump API

Prior, Abandoned Approaches

Chrome (speculative syntax, pass --enable-blink-features=AccessibilityObjectModel):

var c = await window.getComputedAccessibleNode(element);
console.log(c.role);
console.log(c.label);

Firefox (out of date syntax, about:config accessibility.AOM.enabled = true):

console.log(element.accessibleNode.computedRole);