Is Variant-in-Variant significant?
Comparing http://www.isotopicmaps.org/sam/sam-model/ and http://www.isotopicmaps.org/sam/sam-xtm/ it looks like the model does not allow nesting of <variant> within <variant>, but the syntax does.
Given that each <variant> still needs parameters, this makes sense, but it makes it impossible to generate nested <variant> elements.
Resolution: No nested variants in my database.