lib/metanorma/itu/biblio.rng in metanorma-itu-2.5.1 vs lib/metanorma/itu/biblio.rng in metanorma-itu-2.5.2

@@ -1202,10 +1202,12 @@
         </attribute>
       </optional>
       <optional>
         <ref name="formattedref"/>
       </optional>
-      <ref name="btitle"/>
+      <oneOrMore>
+        <ref name="btitle"/>
+      </oneOrMore>
       <optional>
         <ref name="bplace"/>
       </optional>
       <optional>
         <ref name="seriesorganization"/>