diff --git a/xml/rule-3.9.rng b/xml/rule-3.9.rng
index 4cbefa7f0d..15c487d4da 100644
--- a/xml/rule-3.9.rng
+++ b/xml/rule-3.9.rng
@@ -1,233 +1,235 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <grammar xmlns="http://relaxng.org/ns/structure/1.0" 
          xmlns:ann="http://relaxng.org/ns/compatibility/annotations/1.0"
          datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes">
   <start>
       <ref name="element-rule"/>
   </start>
 
   <define name="element-rule">
     <element name="rule">
       <choice>
         <attribute name="id-ref"><data type="IDREF"/></attribute>
         <group>
           <attribute name="id"><data type="ID"/></attribute>
-          <choice>
-            <externalRef href="score.rng"/>
-            <attribute name="score-attribute"><text/></attribute>
-          </choice>
+          <optional>
+            <choice>
+              <externalRef href="score.rng"/>
+              <attribute name="score-attribute"><text/></attribute>
+            </choice>
+          </optional>
           <optional>
             <attribute name="boolean-op">
               <choice>
                 <value>or</value>
                 <value>and</value>
               </choice>
             </attribute>
           </optional>
           <optional>
             <attribute name="role"><text/></attribute>
           </optional>
           <oneOrMore>
             <choice>
               <ref name="expression"/>
               <ref name="date_expression"/>
               <ref name="rsc_expression"/>
               <ref name="op_expression"/>
               <ref name="element-rule"/>
             </choice>
           </oneOrMore>
         </group>
       </choice>
     </element>
   </define>
 
   <!-- A node attribute expression -->
   <define name="expression">
     <element name="expression">
       <attribute name="id"><data type="ID"/></attribute>
       <attribute name="attribute"><text/></attribute>
       <attribute name="operation">
         <choice>
           <value>lt</value>
           <value>gt</value>
           <value>lte</value>
           <value>gte</value>
           <value>eq</value>
           <value>ne</value>
           <value>defined</value>
           <value>not_defined</value>
         </choice>
       </attribute>
       <optional>
         <attribute name="value"><text/></attribute>
       </optional>
       <optional>
         <attribute name="type" ann:defaultValue="string">
           <choice>
             <value>string</value>
             <value>integer</value>
             <value>number</value>
             <value>version</value>
           </choice>
         </attribute>
       </optional>
       <optional>
         <attribute name="value-source" ann:defaultValue="literal">
           <choice>
             <value>literal</value>
             <value>param</value>
             <value>meta</value>
           </choice>
         </attribute>
       </optional>
     </element>
   </define>
 
   <define name="date_expression">
     <element name="date_expression">
       <attribute name="id"><data type="ID"/></attribute>
       <choice>
         <group>
           <attribute name="operation"><value>in_range</value></attribute>
           <choice>
             <attribute name="start"><text/></attribute>
             <attribute name="end"><text/></attribute>
             <group>
               <attribute name="start"><text/></attribute>
               <attribute name="end"><text/></attribute>
             </group>
           </choice>
           <optional>
             <ref name="duration"/>
           </optional>
         </group>
         <group>
           <attribute name="operation"><value>gt</value></attribute>
           <attribute name="start"><text/></attribute>
         </group>
         <group>
           <attribute name="operation"><value>lt</value></attribute>
           <attribute name="end"><text/></attribute>
         </group>
         <group>
           <attribute name="operation"><value>date_spec</value></attribute>
           <ref name="date_spec"/>
         </group>
       </choice>
     </element> 
   </define>
 
   <define name="rsc_expression">
     <element name="rsc_expression">
       <attribute name="id"><data type="ID"/></attribute>
       <optional>
         <attribute name="class"><text/></attribute>
       </optional>
       <optional>
         <attribute name="provider"><text/></attribute>
       </optional>
       <optional>
         <attribute name="type"><text/></attribute>
       </optional>
     </element>
   </define>
 
   <define name="op_expression">
     <element name="op_expression">
       <attribute name="id"><data type="ID"/></attribute>
       <attribute name="name"><text/></attribute>
       <optional>
         <attribute name="interval"><text/></attribute>
       </optional>
     </element>
   </define>
 
   <define name="duration">
     <element name="duration">
       <attribute name="id"><data type="ID"/></attribute>
       <optional>
         <attribute name="years"><text/></attribute>
       </optional>
       <optional>
         <attribute name="months"><text/></attribute>
       </optional>
       <optional>
         <attribute name="weeks"><text/></attribute>
       </optional>
       <optional>
         <attribute name="days"><text/></attribute>
       </optional>
       <optional>
         <attribute name="hours"><text/></attribute>
       </optional>
       <optional>
         <attribute name="minutes"><text/></attribute>
       </optional>
       <optional>
         <attribute name="seconds"><text/></attribute>
       </optional>
 
       <!-- @COMPAT: The below attributes are invalid for duration -->
       <optional>
         <attribute name="monthdays"><text/></attribute>
       </optional>
       <optional>
         <attribute name="weekdays"><text/></attribute>
       </optional>
       <optional>
         <attribute name="yearsdays"><text/></attribute>
       </optional>
       <optional>
         <attribute name="weekyears"><text/></attribute>
       </optional>
       <optional>
         <attribute name="moon"><text/></attribute>
       </optional>
     </element>
   </define>
 
   <define name="date_spec">
     <element name="date_spec">
       <attribute name="id"><data type="ID"/></attribute>
       <optional>
         <attribute name="years"><text/></attribute>
       </optional>
       <optional>
         <attribute name="months"><text/></attribute>
       </optional>
       <optional>
         <attribute name="monthdays"><text/></attribute>
       </optional>
       <optional>
         <attribute name="hours"><text/></attribute>
       </optional>
       <optional>
         <attribute name="minutes"><text/></attribute>
       </optional>
       <optional>
         <attribute name="seconds"><text/></attribute>
       </optional>
       <optional>
         <attribute name="yeardays"><text/></attribute>
       </optional>
       <optional>
         <attribute name="weekyears"><text/></attribute>
       </optional>
       <optional>
         <attribute name="weeks"><text/></attribute>
       </optional>
       <optional>
         <attribute name="weekdays"><text/></attribute>
       </optional>
       <optional>
         <attribute name="moon"><text/></attribute>
       </optional>
 
       <!-- @COMPAT: The below attributes are invalid for date_spec -->
       <optional>
         <attribute name="yearsdays"><text/></attribute>
       </optional>
     </element>
   </define>
 
 </grammar>