2.2.1.4 Resource List Content-Type
If the client sends an HTTP Accept header ([RFC7231] section 5.3.2) requesting the "application/x-msts-radc+xml" and content compatible with schema version 2.0 (see section 2.2.5), the server SHOULD set the Content-Type of the response resource list as "application\x-msts-radc+xml". Otherwise, the server MUST set the Content-Type of the response resource list as "text/xml".<5>