A Boolean value that indicates whether the synthesizer is speaking.
- iOS 7.0+
- macOS 10.14+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 3.0+
true if the synthesizer is speaking or has utterances enqueued to speak, even if it is currently paused. Returns
false if the synthesizer has finished speaking all utterances in its queue or if it has not yet been given an utterance to speak.