Resources xml files - schema, layout, documentation?

Hey there folks, got another one for you.

It seems like the resources files can be anywhere in resources/, and as long as they end in ".xml" and follow some(?) format they're automatically picked up. The docs sorta talk about these files ( https://developer.garmin.com/connect-iq/core-topics/resources ), and there are code samples provided by the SDK, but it's missing a lot of info and I want to dig into the details here. Also nowhere does it mention <fonts>, <drawables>, or really much anything about any root tags other than <resources> -- how do these work together?

Where is the definition for this format? Do you have an XSD, RNG, or some other spec file somewhere? Any way to validate these files? What are the allowed root tags, can they be nested, what are the options for each node type? I'm looking at making a build script to generate some of this stuff automatically, and having a spec would be incredibly helpful.