A conformance clause is not a substitute for regular normative content. Points 3 and 4 in the conformance clause :

("The <

{aggregate prefix}:Payload element SHALL have one or the other of the <{aggregate prefix}

:PayloadContent> element child or the <

{aggregate prefix}

:PayloadExternalReference> element child (that is, it MUST NOT have both).", etc.)

are really just regular normative content, and should be in the main body of the specification - e.g. in section 3.5.3. Then the conformance clause refers to these either directly or indirectly (e.g. refers to the section) and asks for the BDE to satisfy these requirements or constraints.