Spec says: It is a schema definition error if any children have their dfdl:initiator property set to the empty string. Does that include a sequence with a hiddenGroupRef? For example, part of a schema for email headers is this: <xsd:choice dfdl:initiatedContent="yes"> <xsd:element ref="Date"/> <xsd:element ref="From"/> <xsd:element ref="MessageId"/> <xsd:element ref="Subject"/> <!-- all unknown and unwanted headers --> <xsd:sequence dfdl:hiddenGroupRef="UnwantedHeadersGroup"/> </xsd:choice> Date, From, and the other headers are all elements with initiators, but UnwantedHeadersGroup does not have an initiator (because I don't know it a priori). Should this throw an error in a DFDL implementation? I suspect it should, though I hope it shouldn't.