Requirements in Section 4 are unclear

The conformance clause refers to Section 4, which itself only points at Appendix A, which contains a schema. (why not put this schema in Section 4?)
The conformance clause says"
"An XML 1.0 element is a conforming EDXL-HAVE-v2.0 Message if and only if: a) it meets the general requirements specified in Section 4..."
But the Requirements in Section 4 are unclear
In fact, there is no clear requirement in Section 4. In the referred appendix there are tables with annotations that decorate the schema, some of these annotations use "should". Do such annotations contain the requirements? Is the requirement to validate against the schema? Then why not say so?