grammars/gbstandard.rng in relaton-gb-1.8.1 vs grammars/gbstandard.rng in relaton-gb-1.9.0

@@ -58,9 +58,12 @@
     </define>
     <define name="BibDataExtensionType">
       <optional>
         <ref name="doctype"/>
       </optional>
+      <optional>
+        <ref name="docsubtype"/>
+      </optional>
       <zeroOrMore>
         <ref name="gbcommittee"/>
       </zeroOrMore>
       <zeroOrMore>
         <ref name="ics"/>