Right, this is pretty much exactly what I meant by XML started with all the complexity that other things will add. I will happily cede that data is a huge area

Right, this is pretty much exactly what I meant by XML started with all the complexity that other things will add. I will happily cede that data is a huge area where "duck typing" is far and away the correct choice. Taxonomies of data fail all the time. With odd rules that are largely defined by their exceptions.