indicator

The indicator part role marks an element as a decorative representation of state — a check glyph inside a checkbox, the thumb of a switch, the chevron on a disclosure.

Why it matters

This is the one part whose job is subtraction, and it prevents a specific and common double-announcement. A checkbox with a check glyph already announces “checked” through aria-checked or the native input. If the glyph also exposes itself — as an image with a filename, or as a text node containing a character — the same fact is announced twice, and the second announcement is usually noise like “checkmark graphic.”

Without the role, the transform has no way to distinguish a glyph that means something from a glyph that merely draws the state, so it must either hide all of them or none.

Emission

Scaffold

Where	What is emitted
The indicator element itself	`aria-hidden="true"`
The resolved control	Nothing

The element’s tag, classes, layout, and styling are unchanged. Only the attribute is added, so nothing about the visual result changes.

An aria-hidden element must not contain focusable content. An indicator whose subtree contains a slot or an interactive element is a warning: hiding it would strand the focusable descendant in a region assistive technology cannot see.

Contract

None. Most parts add an id to their own element and an attribute to a different element; indicator touches only itself, and the control gains nothing. Either way a part is wiring, not behavior — the only parts that carry handlers are increment and decrement, which call stepUp() / stepDown() on their control.

An indicator is decoration by declaration. If an element needs a handler it is not an indicator — it is a button or an increment / decrement part.

How it resolves

indicator is accepted by both value-bearing and non-value-bearing control concepts, so it follows the standard two-path rule:

Where the component’s single value-bearing control accepts it (checkbox, radio, switch), the part resolves to that control regardless of tree position.
Where only non-value-bearing concepts accept it (button, togglebutton, disclosure), it resolves by proximity, and ambiguity is an error naming every candidate.

In practice resolution rarely matters for this part, because the emission does not depend on which control it resolved to — aria-hidden="true" is the same attribute either way. Resolution matters only for validating that the part is accepted at all.

Platforms

	Emits	Behavior a user gets
Web	`aria-hidden="true"`	Screen readers skip the glyph; the state announces once, from the control
iOS	The glyph hidden from accessibility	VoiceOver skips the glyph and announces the state once, from the control
Android	The glyph’s semantics cleared	TalkBack skips the glyph and announces the state once, from the control

Before and after

Without the role:

{/* … */}
<span className="check" data-element="checkGlyph" />
{/* … */}

With the role:

{/* … */}
<span className="check" data-element="checkGlyph" aria-hidden="true" />
{/* … */}