Unwind mechanism

[Duggan]

I was poking around with creating an XSD file to validate system file input (I have to use XSD in my current job, so I'm trying to practice on the side), and I noticed that "unwind" attribute in Component, which has a redlink to an Advanced topic on unwind mechanisms, admittedly one of several in that section of the wiki. Is there anything going on more complicated than a tag group?

I did a quick poke around the files I have source for, and everything I've found is a copy-paste from the sample data, pointing to the Identity tag "IsAdvance". Is it a simply binary of "Is this tag present? If so, we can unwind" or is there the possibility of setting up a more complex script to figure out how things unwind?

This is an idle curiosity question, as much as anything else. Feel free to just tell me "it's complicated".