Thread:StephenTX/@comment-25046890-20160206080318/@comment-10228869-20160208070522

Sure you can nest them; see early versions of Template:Navbox/doc and Template:Navbox with collapsible groups/doc before my "simplify example" edits. I looked at your sandbox and it seems the only problem was "list␣1" rather than "list1" in the inner navbox; I didn't save my edits, but the preview looked fine to me with that fixed.

FWIW, Module:Navbox doesn't have the 20 group limit; I need to fix the CSS classes it uses before I can promote Template:Navbox/sandbox, but you can use that in the meantime if you don't mind the styles being a bit off.