Announcer, AriaLiveAnnouncer, and SpeechSynthesisAnnouncer

An Announcer (from scenerystack/utterance-queue) is the output side of UtteranceQueue: the queue resolves an Utterance's alert content, then calls announcer.announce( utterance, resolvedResponse ). Concrete subclasses implement how the text reaches the user — via hidden aria-live elements (AriaLiveAnnouncer) or the browser's Web Speech API (SpeechSynthesisAnnouncer).

import {
  UtteranceQueue,
  AriaLiveAnnouncer,
  SpeechSynthesisAnnouncer,
  Utterance
} from 'scenerystack/utterance-queue';

A minimal example — AriaLiveAnnouncer

Interactive Description alerts typically use AriaLiveAnnouncer, which cycles through a small pool of off-screen <p aria-live="…"> elements to avoid VoiceOver interrupting consecutive alerts:

const announcer = new AriaLiveAnnouncer();
document.body.appendChild( announcer.ariaLiveContainer ); // required once

const queue = new UtteranceQueue( announcer );
queue.addToBack( new Utterance( { alert: 'Temperature increased' } ) );

A minimal example — SpeechSynthesisAnnouncer

Voicing features use SpeechSynthesisAnnouncer, which drives window.speechSynthesis:

const announcer = new SpeechSynthesisAnnouncer();
await announcer.initialize(); // picks a voice, handles browser quirks

const queue = new UtteranceQueue( announcer );
queue.addToBack( new Utterance( { alert: 'Beaker is half full' } ) );

Shared Announcer contract

Member	Description
readyToAnnounce	When false, UtteranceQueue waits before sending the next utterance — subclasses set this while output is in progress
hasSpoken	Whether this announcer has successfully spoken at least once (used to gate first-speech initialization)
announcementCompleteEmitter	Subclasses emit when a given Utterance finishes speaking so the queue can dequeue the next one
respectResponseCollectorProperties	Whether ResponsePacket alerts honor responseCollector feature toggles (Interactive Description vs. Voicing)

Announcer extends PhetioObject and is abstract — simulation code normally receives a configured instance from the framework rather than subclassing it.

AriaLive priority

AriaLiveAnnouncer accepts an ariaLivePriority option on each announce() call, using the AriaLive enumeration:

Value	Effect
AriaLive.POLITE	Updates a polite aria-live region — waits for a pause in screen-reader speech
AriaLive.ASSERTIVE	Updates an assertive region — interrupts current speech

Choosing an announcer

Class	Channel	Typical use
AriaLiveAnnouncer	Hidden DOM aria-live regions	Interactive Description alerts independent of focus
SpeechSynthesisAnnouncer	Web Speech API	Voicing spoken responses

Both plug into the same UtteranceQueue API — the queue handles timing, priority, and stability; the announcer handles platform output.