Granite UI "Composite" Form Field

Is there such a thing out of the box? Looking at the render.jsp of granite/ui/components/foundation/form/multifield, the comments say the following:

"If the field is a composite, it is its responsibility to concatenate the fields into one, before the form gets submitted, and to separate them again on rendering."

I'm just wondering if there's some example of this anywhere in the current codebase or if anyone has written one. I've searched for and read all of the forum posts and blog posts online about "Custom composite multifields for TouchUI" but they really don't do exactly what I expected or need. I've written xtypes in the past that are perfect, but unfortunately, I can't use those in TouchUI.

I think the closest I've seen to what I need to accomplish is Cognifide's Multifield II approach, which can be seen here. The only difference would be instead of storing these values as child nodes, I'm trying to store them as a String[] property with a JSON Object stored as a string in each multi-value. Think the Quiz component that Praveen Dubey wrote, but with a Coral/GraniteUI native dialog, instead of still relying on ExtJS xtypes.

I suppose this wouldn't be nearly as difficult as I'm imagining it would be, if I understood the Granite foundation form component structure better. I'm still all brand new to this, still so used to the "old way".