ARIA element reference reflection — writable setters

The ARIAMixin interface exposes writable IDL attributes that take element references directly instead of ID strings. Setting one wires up an ARIA relationship without either element needing an id, and works across shadow-root boundaries where the old IDREF attributes cannot. This page tests all of them — see the reflection explainer.

Cross-shadow-root demo (impossible with IDREFs)

Inside #host’s shadow tree, a button sets ariaLabelledByElements to a <label> that lives in the outer light DOM — a reference that points out of the shadow tree. IDREF strings can’t cross that boundary; element references can.