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.