A bird's-eye view of the Mozilla framework
an nsirdfnode must be an nsirdfliteral or an nsirdfresource.
... getlink() uses the nsirdfservice to obtain an nsirdfresource for the requested link.

nsIDOMXULElement
resource nsirdfresource read only.
... returns the nsirdfresource corresponding to the element's ref or id attribute, if any.

nsIXULTemplateBuilder
de); void removeresult(in nsixultemplateresult aresult); void replaceresult(in nsixultemplateresult aoldresult, in nsixultemplateresult anewresult, in nsidomnode aquerynode); void resultbindingchanged(in nsixultemplateresult aresult); nsixultemplateresult getresultforid(in astring aid); nsixultemplateresult getresultforcontent(in nsidomelement aelement); boolean hasgeneratedcontent(in nsirdfresource anode, in nsiatom atag); void addrulefilter(in nsidomnode arule, in nsixultemplaterulefilter afilter); [noscript] void init(in nsicontent aelement); [noscript] void createcontents(in nsicontent aelement, in boolean aforcecreation); void addlistener(in nsixulbuilderlistener alistener); void removelistener(in nsixulbuilderlistener alistener); attributes attribute type description ...
...boolean hasgeneratedcontent( in nsirdfresource anode, in nsiatom atag ); parameters anode node to check.

resource - Archive of obsolete content
« xul reference resource type: nsirdfresource returns an rdf resource with the value of the element's ref attribute.

RDF in Mozilla FAQ - Archive of obsolete content
nsirdfresource getsource(aproperty, atarget, atruthvalue).

JavaScript Tips
instead, use instanceof, e,g,: if (target instanceof components.interfaces.nsirdfresource) return target.value; if (target instanceof components.interfaces.nsirdfliteral) return target.value; return null; don't test the return value of queryinterface, it always returns the original variable if it succeeds.

nsIMicrosummaryService
in the old rdf-based bookmarks datastore, bookmark ids are nsirdfresource objects.

nsIXULTemplateResult
resource nsirdfresource resource for the result, which may be null.