rrm:isHeading always false, even for Heading and Module Heading

I am using the RESTful API to query a module from DOORS NG 5.0.2.  My query is of the form

http://.../rm/publish/resources?resourceURI=_IDENxyz000

The result shows all the items in the module but every entry has

<rrm:isHeading>false</rrm:isHeading>

even for those that are of Type "Module Heading" and "Heading" (just to cover all cases).

How can I determine if the object is a Heading?  I was using "if has child, then heading" but that does not work for Headings with no children (sections with no contents).

I am also querying the referenced object (that appears in the "Module Name artifacts" collection).  That appears provide nothing to indicate heading either.