> example :: VoiceTwiml
> example =
>   response $ do
>     play' Nothing $ def & digits .~ Just [W, W, W, W, D3]
>     end
>   where Twiml.Syntax{..} = def

>>> show example
<?xml version="1.0" encoding="UTF-8"?>
<Response>
  <Play digits="wwww3" />
</Response>