Can you point me in the direction to learn how to bind multiple custom XML nodes to a drop-down content control?

I can see in custom XML from Word files that have been in a SharePoint document library with multi-selection list items that the drop-downs are functional in the Word file's doc properties. But the SharePoint-sourced XML is inscrutable to me, and I haven't been able to successfully emulate the structure.

A video by former MS employee Eric White walks through the process but isn't getting me all the way there; an article and example doc are no longer on Microsoft's site and unavailable via archive.org.

Microsoft's current instructions include using Visual Studio (which I have), but the method uses C#, so it's beyond me.