tolyo

Looking at the [global attributes spec](https://github.com/yoshuawuyts/html/blob/main/resources/manual/global_attributes.json), we have only three types: `String`, `Integer`, and `Bool`. For the `String` type, what would be the strategy to support [enumerated attributes](https://html.spec.whatwg.org/dev/common-microsyntaxes.html#enumerated-attribute)?