Document Conformance
Document conformance is purely syntactic; it involves only Items 1 and 2 in §2.3 above.
A conforming document shall conform to the schema (Item 1) and any additional syntax constraints (Item 2).
The document character set shall conform to the Unicode Standard and ISO/IEC 10646-1, with either the UTF-8 or UTF-16 encoding form, as required by the XML 1.0 standard.
Any XML element or attribute not explicitly included in this Standard shall use the extensibility mechanisms described by Parts 4 and 5 of this Standard.