Registration for Reference Target for Cross-Root ARIA

Explainer: https://github.com/WICG/webcomponents/blob/gh-pages/proposals/reference-target-explainer.md

Intent: https://groups.google.com/a/chromium.org/g/blink-dev/c/C3pELgMqzCY/m/Lpb6DkueAQAJ

Origin Trial: https://developer.chrome.com/origintrials/#/view_trial/2164542570904944641

Spec: TBD

Other Resources:

• Solving Cross-root ARIA Issues in Shadow DOM
• How Shadow DOM and accessibility are in conflict

=== This is a demo of Reference Target for Cross-Root ARIA. ===

=== Phase 1 adds the ability to designate a single element as the target for all IDREF properties that refer to the host. ===

// shadowrootreferencetarget

// referenceTarget attribute on the ShadowRoot object,

=== (Not implemented yet!) Phase 2 adds a way to re-target specific properties (like aria-activedescendant) to refer a separate element. ===

// ShadowRoot referenceTargetMap attribute