nValidity and
well-formedness are XML 1.0 concepts
äThey are defined over character sequences
nNamespace-compliant is a Namespace concept
äIt's defined over character sequences too
nSchema-validity is the XML Schema concept
äIt is defined over XML document Infosets
nSo the whole XML Schema
exercise is predicated on and layered on top of XML 1.0 well-formedness
plus Namespaces
äBecause they are constitutive of the Infoset
