The spec says that <node> may contain both <instance_geometry> and other <node> elements. Nevertheless, I think that <instance_geometry> elements appear in leaf <node> elements only, though the spec says nothing about this.
By exploring several .dae files, I see that my thought is correct.
So do you know whether it is mandatory for <instance_geometry> appear inside leaf <node>s only?
Thanks for your answers in advance.