Review of XForms 2.0 sections 4-6

All,
 
First, I am wondering in which section XForms-specific XPath functions, such as
instance(), is-card-number(),..., are now listed and described?
 
At "6.1 Model Item Property Definitions", I am not convinced that allowing
multiple type properties is effectively a good idea. For implementors, this
means multiple types per node. For authors, it might be better to explicitly
define extra types. Anyone with a use case??


 

Thanks!
 
-Alain