Can't you use default_tag() to do this?

I was trying to narrow the scope of when the default tag is applied just in case there were any unknown side effects, but I can try using default_tag() instead.

Ah, I see how to use default_tag() to do the same thing now. The documentation for it wasn't clear.

The hinge still has a problem as shown by top_half(z=4.8):

Some extra material is connecting the two sides of the hinge together.

That part is from the extra backstop that I added. It goes away without the second (attached) child, which I've adjusted in my design.

Would it suffice to clarify default_tag if I changed the description to "conditionally set a default tag"?

The description was fine, I just didn't see the argument in the module signature (in the usage section) even though it was in the argument descriptions. But if you're in there doing other things and wanted to update the description, it wouldn't hurt.

I can update the docs and the update will merge someday.