The XML Schema worldview
 
  - Validity and well-formedness are XML 1.0 concepts.
   
    - They are defined over character sequences.
 
- Namespace-compliant is a Namespace concept.
   
    - It's defined over character sequences too.
 
- Schema-validity assessment is the XML Schema concept.
   
    - It is defined in terms of XML document Infosets.
 
- So the whole XML Schema exercise is predicated on and layered on top of
XML 1.0 well-formedness plus Namespaces.
   
    - Because they are constitutive of the Infoset.