Juju docs for configuration options seem old and incomplete

I've been looking for some guidance on exposing configuration options from a charm. The only information I found was
https://juju.ubuntu.com/docs/drafts/service-config.html. It doesn't give an example of data types supported in config.yaml (int, string...?) . Also in the example on that page there are config options without a dataype type set (like username), is that supported ? I know the guide is in the draft section but more information on how to expose configuration options would be great