That title is a mouthful. And many might not be familiar with what it means. Check out this video to learn more about Mura's Form Builder, or you can go to this link which goes directly to the section of the video that I had an issue with.
In the video, Sean demonstrates the basics of creating a dropdown where you can manually enter the options for the dropdown. He does gloss over the fact that you can also get the data for the dropdown from other sources. Unfortunately, this is the extent of the currently existing documentation for this feature. So when I wanted to use this feature of the form builder to feed in data from another part of the site, I had to figure it out on my own. Here is what I came up with. Hopefully it is right(ish). Oh, you can also use this stuff to populate checkbox and radio button sets.