https://dvcs.w3.org/hg/speech-api/raw-file/tip/speechapi.html
This is the spec that is implemented
https://dvcs.w3.org/hg/speech-api/raw-file/9a0075d25326/speechapi.html#tts-section
Not that on iOS, speech will not be uttered unless the user performs an action to make it happen... like click a button.
This is similar to how web audio is implemented on iOS