FW: A quesiton on XPath-datamodel (Mapping PSVI addition to Node Properties)

I encountered some problem when reading the spec of XQuery 1.0 and XPath 2.0 Data Model (XDM).

http://www.w3.org/TR/xpath-datamodel/#PSVI2Types

In the Chapter 3.3.1 ( Mapping PSVI addition to Node Propterties), it says:

• The [validity] and [validation attempted] properties exist and have the values "valid" and "full", respectively, the schema type of an element or attribute information item is represented by an expanded-QName whose namespace and local name correspond to the first applicable items in the following list:
• If the declared type exists and is a union and the actual type is …..
• If there is no declared type, and the actual type is a union, then: ……
• Otherwise: ……

Regarding the second bullet, I can NOT understand in which cases there will be no declared type?  I think it is impossible. Since the declared type reference the [type definition] associated with the declaration,  if an element/attribute is validated, it should be already associated with a element/attribute declaration, which should have the type definition.

Does anyone know it and  give me some clarification on this?  Thanks a lot in advance!