[Accessibility] TTS API interface description + reqs update

[Jonathan Duddington]

In article <1146313875.4101.138.camel at chopin>,
   Hynek Hanke <hanke at brailcom.org> wrote:

> I'll be thankful for any comments about the new interface draft
> and about the updated requirements.

  voice_descriptor_t* list_voices(char *driver_id)

... returns a list of voice descriptors.
How is the list terminated?

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