Joseph Wright wrote:
> 2) Exact structure for type/template boundary (I still don't get it!)

A hunt through some more of the xpackages gives me an example where
perhaps I can see this.  From xfmgalley.dtx:

\DeclareTemplateType{pshape}{0}
\DeclareTemplate{pshape}{cutout}{0}{ <keys> } { <code> }
\DeclareInstance{pshape}{staggered}{cutout}{ <keys>}

So, taking Will's ordering we have:

pshape -> cutout -> staggered

This sort-of makes sense. (There are other examples in the same place:
perhaps it is needed after all!)
-- 
Joseph Wright