Non-normative content in 4.2.2. Constructing a Schema Document Subset

[TomCarlson-NTAC]

Section 4.2.2. Constructing a Schema Document Subset is non-normative and could be moved to a different document. Definition of schema document subset in 4.2.1. Basic Subset Concepts is also non-normative and should be tightened.

[TomCarlson-NTAC]

Pushed off until a revamped version is in progress. Left open until then.