The default read-only property of the SpeechSynthesisVoice interface returns a Boolean indicating whether the voice is the default voice for the current app (true), or not (false.)
The localService read-only property of the SpeechSynthesisVoice interface returns a Boolean indicating whether the voice is supplied by a local speech synthesizer service (true), or a remote speech synthesizer service (false.)
The voiceURI read-only property of the SpeechSynthesisVoice interface returns the type of URI and location of the speech synthesis service for this voice.
The onerror property of the SpeechSynthesisUtterance interface represents an event handler that will run when an error occurs that prevents the utterance from being succesfully spoken (when the error event fires.)