In reply to Weston Ruter.

Exactly. I was able to mostly use the "standard" set of options (partly to keep things consistent), but had a few use cases that needed more than the basics.

I've been reading and re-reading the Customizer JS, and it is pretty deep. Right now, the documents refer readers to some of the custom code in Twenty Fifteen or Sixteen. I'd really like to see a well documented case study of implementing a single custom control via the JS interfact - say a custom labelled push-buttons on a row alternative to vertically stacked radio buttons. (Such a control would be really nice for things like font controls, or bg image layouts).

But mostly, it is getting me to finally get beyond the basics of JS (which really are plenty for most postMessage based Customizer controls.) Gotta look into that selective refreshing....