While technically the library could continue supporting custom SSML, I ended up removing it because keeping the support was pointless. The API stopped allowing

While technically the library could continue supporting custom SSML, I ended up removing it because keeping the support was pointless. The API stopped allowing anything other than the basic tags used by Microsoft Edge itself (i.e., prosody for rate/volume/pitch, voice, etc). As for comparable projects, you can use Azure's offerings instead. They have a free tier that's really generous.