diff --git a/cts/schemas/test-3/ref/duplicate-nvpairs-no-default.ref-2 b/cts/schemas/test-3/ref/duplicate-nvpairs-no-default.ref-2
index 2d9a5882ba..9f0abd6d13 100644
--- a/cts/schemas/test-3/ref/duplicate-nvpairs-no-default.ref-2
+++ b/cts/schemas/test-3/ref/duplicate-nvpairs-no-default.ref-2
@@ -1,49 +1,41 @@
 <cib crm_feature_set="3.19.7" validate-with="pacemaker-4.0" epoch="8" num_updates="0" admin_epoch="0" original="1">
   <configuration original="1">
     <!-- The essential elements of this test are:
          * There is one of each kind of several nvset element
            (cluster_property_set, instance_attributes, meta_attributes,
            utilization).
          * Each nvset contains multiple nvpairs with the same name, as well as
            one nvpair with a different name.
          * There are no nvpairs with value="#default".
          * One nvset uses id-refs.
 
          In this situation, only the first nvpair with a given name in a given
          nvset should be kept. Any subsequent ones should be dropped.
       -->
     <crm_config original="1">
       <cluster_property_set id="cib-bootstrap-options" original="1">
         <nvpair id="cib-bootstrap-options-option1" name="option" value="value1" original="1"/>
-        <nvpair id="cib-bootstrap-options-option2" name="option" value="value2" original="1"/>
-        <nvpair id="cib-bootstrap-options-option3" name="option" value="value3" original="1"/>
         <nvpair id="cib-bootstrap-options-other-option" name="other-option" value="value0" original="1"/>
       </cluster_property_set>
     </crm_config>
     <nodes original="1"/>
     <resources original="1">
       <primitive class="ocf" id="rsc1" provider="heartbeat" type="apache" original="1">
         <instance_attributes id="rsc1-instance_attributes" original="1">
           <nvpair id="rsc1-instance_attributes-option1" name="option" value="value1" original="1"/>
-          <nvpair id="rsc1-instance_attributes-option2" name="option" value="value2" original="1"/>
           <nvpair id="rsc1-instance_attributes-other-option" name="other-option" value="value0" original="1"/>
-          <nvpair id="rsc1-instance_attributes-option3" name="option" value="value3" original="1"/>
         </instance_attributes>
         <meta_attributes id="rsc1-meta_attributes" original="1">
           <nvpair id="rsc1-meta_attributes-option1" name="option" value="value1" original="1"/>
           <nvpair id="rsc1-meta_attributes-other-option" name="other-option" value="value0" original="1"/>
-          <nvpair id="rsc1-meta_attributes-option2" name="option" value="value2" original="1"/>
-          <nvpair id="rsc1-meta_attributes-option3" name="option" value="value3" original="1"/>
         </meta_attributes>
         <utilization id="rsc1-utilization" original="1">
           <nvpair id="rsc1-utilization-other-option" name="other-option" value="valueX" original="1"/>
           <nvpair id="rsc1-meta_attributes-option1" name="option" value="value1" original="0"/>
-          <nvpair id="rsc1-utilization-option2" name="option" value="valueB" original="1"/>
-          <nvpair id="rsc1-meta_attributes-option3" name="option" value="value3" original="0"/>
         </utilization>
       </primitive>
     </resources>
     <constraints original="1"/>
   </configuration>
   <status original="1"/>
 </cib>
diff --git a/cts/schemas/test-3/ref/duplicate-nvpairs-no-default.ref-99 b/cts/schemas/test-3/ref/duplicate-nvpairs-no-default.ref-99
index dfd3a7b59e..cf5b98aec0 100644
--- a/cts/schemas/test-3/ref/duplicate-nvpairs-no-default.ref-99
+++ b/cts/schemas/test-3/ref/duplicate-nvpairs-no-default.ref-99
@@ -1,49 +1,41 @@
 <cib crm_feature_set="3.19.7" validate-with="pacemaker-4.0" epoch="8" num_updates="0" admin_epoch="0">
   <configuration>
     <!-- The essential elements of this test are:
          * There is one of each kind of several nvset element
            (cluster_property_set, instance_attributes, meta_attributes,
            utilization).
          * Each nvset contains multiple nvpairs with the same name, as well as
            one nvpair with a different name.
          * There are no nvpairs with value="#default".
          * One nvset uses id-refs.
 
          In this situation, only the first nvpair with a given name in a given
          nvset should be kept. Any subsequent ones should be dropped.
       -->
     <crm_config>
       <cluster_property_set id="cib-bootstrap-options">
         <nvpair id="cib-bootstrap-options-option1" name="option" value="value1"/>
-        <nvpair id="cib-bootstrap-options-option2" name="option" value="value2"/>
-        <nvpair id="cib-bootstrap-options-option3" name="option" value="value3"/>
         <nvpair id="cib-bootstrap-options-other-option" name="other-option" value="value0"/>
       </cluster_property_set>
     </crm_config>
     <nodes/>
     <resources>
       <primitive class="ocf" id="rsc1" provider="heartbeat" type="apache">
         <instance_attributes id="rsc1-instance_attributes">
           <nvpair id="rsc1-instance_attributes-option1" name="option" value="value1"/>
-          <nvpair id="rsc1-instance_attributes-option2" name="option" value="value2"/>
           <nvpair id="rsc1-instance_attributes-other-option" name="other-option" value="value0"/>
-          <nvpair id="rsc1-instance_attributes-option3" name="option" value="value3"/>
         </instance_attributes>
         <meta_attributes id="rsc1-meta_attributes">
           <nvpair id="rsc1-meta_attributes-option1" name="option" value="value1"/>
           <nvpair id="rsc1-meta_attributes-other-option" name="other-option" value="value0"/>
-          <nvpair id="rsc1-meta_attributes-option2" name="option" value="value2"/>
-          <nvpair id="rsc1-meta_attributes-option3" name="option" value="value3"/>
         </meta_attributes>
         <utilization id="rsc1-utilization">
           <nvpair id="rsc1-utilization-other-option" name="other-option" value="valueX"/>
           <nvpair id-ref="rsc1-meta_attributes-option1"/>
-          <nvpair id="rsc1-utilization-option2" name="option" value="valueB"/>
-          <nvpair id-ref="rsc1-meta_attributes-option3"/>
         </utilization>
       </primitive>
     </resources>
     <constraints/>
   </configuration>
   <status/>
 </cib>
diff --git a/cts/schemas/test-3/ref/duplicate-nvpairs-with-default.ref-2 b/cts/schemas/test-3/ref/duplicate-nvpairs-with-default.ref-2
index 4770101a61..b2e24f4e22 100644
--- a/cts/schemas/test-3/ref/duplicate-nvpairs-with-default.ref-2
+++ b/cts/schemas/test-3/ref/duplicate-nvpairs-with-default.ref-2
@@ -1,75 +1,51 @@
 <cib crm_feature_set="3.19.7" validate-with="pacemaker-4.0" epoch="8" num_updates="0" admin_epoch="0" original="1">
   <configuration original="1">
     <!-- The essential elements of this test are:
          * There is one of each kind of several nvset element
            (cluster_property_set, instance_attributes, meta_attributes,
            utilization).
          * Each nvset contains multiple nvpairs with the same name (two of which
            have value "#default"), as well as one nvpair with a different name.
          * Two nvsets use id-refs.
 
          In this situation:
          * If the last nvpair with a given name in a given nvset has value
            "#default", keep only that one.
          * Otherwise, keep only the first nvpair with a given name in a given
            nvset after the last one with that name and value "#default".
       -->
     <crm_config original="1">
       <cluster_property_set id="cluster-properties1" original="1">
-        <nvpair id="cluster-properties1-option1" name="option" value="#default" original="1"/>
-        <nvpair id="cluster-properties1-option2" name="option" value="#default" original="1"/>
         <nvpair id="cluster-properties1-option3" name="option" value="value3" original="1"/>
-        <nvpair id="cluster-properties1-option4" name="option" value="value4" original="1"/>
-        <nvpair id="cluster-properties1-option5" name="option" value="value5" original="1"/>
         <nvpair id="cluster-properties1-other-option" name="other-option" value="value0" original="1"/>
       </cluster_property_set>
       <cluster_property_set id="cluster-properties2" original="1">
-        <nvpair id="cluster-properties2-option1" name="option" value="#default" original="1"/>
-        <nvpair id="cluster-properties2-option2" name="option" value="value1" original="1"/>
-        <nvpair id="cluster-properties2-option3" name="option" value="#default" original="1"/>
         <nvpair id="cluster-properties2-option4" name="option" value="value4" original="1"/>
-        <nvpair id="cluster-properties2-option5" name="option" value="value5" original="1"/>
         <nvpair id="cluster-properties2-other-option" name="other-option" value="value0" original="1"/>
       </cluster_property_set>
     </crm_config>
     <nodes original="1"/>
     <resources original="1">
       <primitive class="ocf" id="rsc1" provider="heartbeat" type="apache" original="1">
         <instance_attributes id="rsc1-instance_attributes" original="1">
-          <nvpair id="rsc1-instance_attributes-option1" name="option" value="value1" original="1"/>
-          <nvpair id="rsc1-instance_attributes-option2" name="option" value="#default" original="1"/>
           <nvpair id="rsc1-instance_attributes-other-option" name="other-option" value="value0" original="1"/>
-          <nvpair id="rsc1-instance_attributes-option3" name="option" value="#default" original="1"/>
           <nvpair id="rsc1-instance_attributes-option4" name="option" value="value4" original="1"/>
-          <nvpair id="rsc1-instance_attributes-option5" name="option" value="value5" original="1"/>
         </instance_attributes>
         <meta_attributes id="rsc1-meta_attributes" original="1">
-          <nvpair id="rsc1-meta_attributes-option1" name="option" value="value1" original="1"/>
           <nvpair id="rsc1-meta_attributes-other-option" name="other-option" value="value0" original="1"/>
-          <nvpair id="rsc1-meta_attributes-option2" name="option" value="#default" original="1"/>
-          <nvpair id="rsc1-meta_attributes-option3" name="option" value="value3" original="1"/>
-          <nvpair id="rsc1-meta_attributes-option4" name="option" value="#default" original="1"/>
           <nvpair id="rsc1-meta_attributes-option5" name="option" value="value5" original="1"/>
         </meta_attributes>
         <utilization id="rsc1-utilization1" original="1">
           <nvpair id="rsc1-utilization1-other-option" name="other-option" value="valueX" original="1"/>
-          <nvpair id="rsc1-utilization1-option1" name="option" value="valueA" original="1"/>
-          <nvpair id="rsc1-utilization2-option2" name="option" value="valueB" original="0"/>
-          <nvpair id="rsc1-utilization1-option3" name="option" value="#default" original="1"/>
-          <nvpair id="rsc1-utilization1-option4" name="option" value="valueD" original="1"/>
           <nvpair id="rsc1-utilization1-option5" name="option" value="#default" original="1"/>
         </utilization>
         <utilization id="rsc1-utilization2" original="1">
           <nvpair id="rsc1-utilization1-other-option" name="other-option" value="valueX" original="0"/>
-          <nvpair id="rsc1-utilization1-option1" name="option" value="valueA" original="0"/>
-          <nvpair id="rsc1-utilization2-option2" name="option" value="valueB" original="1"/>
-          <nvpair id="rsc1-utilization1-option3" name="option" value="#default" original="0"/>
-          <nvpair id="rsc1-utilization1-option4" name="option" value="valueD" original="0"/>
           <nvpair id="rsc1-utilization1-option5" name="option" value="#default" original="0"/>
         </utilization>
       </primitive>
     </resources>
     <constraints original="1"/>
   </configuration>
   <status original="1"/>
 </cib>
diff --git a/cts/schemas/test-3/ref/duplicate-nvpairs-with-default.ref-99 b/cts/schemas/test-3/ref/duplicate-nvpairs-with-default.ref-99
index 2c82fec17b..b80c05e32e 100644
--- a/cts/schemas/test-3/ref/duplicate-nvpairs-with-default.ref-99
+++ b/cts/schemas/test-3/ref/duplicate-nvpairs-with-default.ref-99
@@ -1,75 +1,51 @@
 <cib crm_feature_set="3.19.7" validate-with="pacemaker-4.0" epoch="8" num_updates="0" admin_epoch="0">
   <configuration>
     <!-- The essential elements of this test are:
          * There is one of each kind of several nvset element
            (cluster_property_set, instance_attributes, meta_attributes,
            utilization).
          * Each nvset contains multiple nvpairs with the same name (two of which
            have value "#default"), as well as one nvpair with a different name.
          * Two nvsets use id-refs.
 
          In this situation:
          * If the last nvpair with a given name in a given nvset has value
            "#default", keep only that one.
          * Otherwise, keep only the first nvpair with a given name in a given
            nvset after the last one with that name and value "#default".
       -->
     <crm_config>
       <cluster_property_set id="cluster-properties1">
-        <nvpair id="cluster-properties1-option1" name="option" value="#default"/>
-        <nvpair id="cluster-properties1-option2" name="option" value="#default"/>
         <nvpair id="cluster-properties1-option3" name="option" value="value3"/>
-        <nvpair id="cluster-properties1-option4" name="option" value="value4"/>
-        <nvpair id="cluster-properties1-option5" name="option" value="value5"/>
         <nvpair id="cluster-properties1-other-option" name="other-option" value="value0"/>
       </cluster_property_set>
       <cluster_property_set id="cluster-properties2">
-        <nvpair id="cluster-properties2-option1" name="option" value="#default"/>
-        <nvpair id="cluster-properties2-option2" name="option" value="value1"/>
-        <nvpair id="cluster-properties2-option3" name="option" value="#default"/>
         <nvpair id="cluster-properties2-option4" name="option" value="value4"/>
-        <nvpair id="cluster-properties2-option5" name="option" value="value5"/>
         <nvpair id="cluster-properties2-other-option" name="other-option" value="value0"/>
       </cluster_property_set>
     </crm_config>
     <nodes/>
     <resources>
       <primitive class="ocf" id="rsc1" provider="heartbeat" type="apache">
         <instance_attributes id="rsc1-instance_attributes">
-          <nvpair id="rsc1-instance_attributes-option1" name="option" value="value1"/>
-          <nvpair id="rsc1-instance_attributes-option2" name="option" value="#default"/>
           <nvpair id="rsc1-instance_attributes-other-option" name="other-option" value="value0"/>
-          <nvpair id="rsc1-instance_attributes-option3" name="option" value="#default"/>
           <nvpair id="rsc1-instance_attributes-option4" name="option" value="value4"/>
-          <nvpair id="rsc1-instance_attributes-option5" name="option" value="value5"/>
         </instance_attributes>
         <meta_attributes id="rsc1-meta_attributes">
-          <nvpair id="rsc1-meta_attributes-option1" name="option" value="value1"/>
           <nvpair id="rsc1-meta_attributes-other-option" name="other-option" value="value0"/>
-          <nvpair id="rsc1-meta_attributes-option2" name="option" value="#default"/>
-          <nvpair id="rsc1-meta_attributes-option3" name="option" value="value3"/>
-          <nvpair id="rsc1-meta_attributes-option4" name="option" value="#default"/>
           <nvpair id="rsc1-meta_attributes-option5" name="option" value="value5"/>
         </meta_attributes>
         <utilization id="rsc1-utilization1">
           <nvpair id="rsc1-utilization1-other-option" name="other-option" value="valueX"/>
-          <nvpair id="rsc1-utilization1-option1" name="option" value="valueA"/>
-          <nvpair id-ref="rsc1-utilization2-option2"/>
-          <nvpair id="rsc1-utilization1-option3" name="option" value="#default"/>
-          <nvpair id="rsc1-utilization1-option4" name="option" value="valueD"/>
           <nvpair id="rsc1-utilization1-option5" name="option" value="#default"/>
         </utilization>
         <utilization id="rsc1-utilization2">
           <nvpair id-ref="rsc1-utilization1-other-option"/>
-          <nvpair id-ref="rsc1-utilization1-option1"/>
-          <nvpair id="rsc1-utilization2-option2" name="option" value="valueB"/>
-          <nvpair id-ref="rsc1-utilization1-option3"/>
-          <nvpair id-ref="rsc1-utilization1-option4"/>
           <nvpair id-ref="rsc1-utilization1-option5"/>
         </utilization>
       </primitive>
     </resources>
     <constraints/>
   </configuration>
   <status/>
 </cib>
diff --git a/cts/schemas/test-3/ref/id-ref.ref-2 b/cts/schemas/test-3/ref/id-ref.ref-2
index 6a43d728dd..d33ffb253e 100644
--- a/cts/schemas/test-3/ref/id-ref.ref-2
+++ b/cts/schemas/test-3/ref/id-ref.ref-2
@@ -1,72 +1,71 @@
 <cib crm_feature_set="3.19.7" validate-with="pacemaker-4.0" epoch="16" num_updates="0" admin_epoch="0" original="1">
   <configuration original="1">
     <!-- The essential elements of this test are:
          * There is a cluster_properties_set element with an id attribute (set
            to cluster-properties1) and a set of nvpair children.
          * There are two cluster_properties_set elements with an id-ref
            attribute (set to cluster-properties1): one before and one after the
            original.
          * There is a primitive resource (rsc1) with a meta_attributes element
            containing nvpair children.
            * The first nvpair is a definition (has an id attribute).
            * The second has an id-ref attribute with no name attribute.
            * The third has id-ref="cluster-properties1-option1" and
              name="option3". Setting both id-ref and name is an undocumented
              feature that allows the same nvpair value to be used with multiple
              names (see commit 3912538 and associated pull request).
 
          In this situation:
          * In the first step of the upgrade transformation pipeline:
            * Each element with an id-ref attribute without a name attribute
              should be replaced by a copy of the element whose id attribute is
              set to the same value, but with the "original" attribute set to 1.
            * Each element with an id-ref attribute and a name attribute should
              be replaced by a copy of the element whose id attribute is set to
              the original id-ref value, except that in the copy:
              * The id attribute begins with $upgrade_prefix and ends with the
                value of @name.
              * The name attribute is overridden by the reference's @name value.
          * In the final step:
            * Resolved references that did not have name attributes should be
              converted back to references.
            * For resolved references that did have name attributes, such that
              the id of the resolved element differs from the original id-ref
              value:
              * The first element with the new id value remains expanded as a
                definition.
              * Any subsequent elements with the new id value are converted to
                references to the first one.
       -->
     <crm_config original="1">
       <cluster_property_set id="cluster-properties1" original="0">
         <nvpair id="cluster-properties1-option1" name="option1" value="value1" original="0"/>
         <nvpair id="cluster-properties1-option2" name="option2" value="value2" original="0"/>
       </cluster_property_set>
       <cluster_property_set id="cluster-properties1" original="1">
         <nvpair id="cluster-properties1-option1" name="option1" value="value1" original="1"/>
         <nvpair id="cluster-properties1-option2" name="option2" value="value2" original="1"/>
       </cluster_property_set>
       <cluster_property_set id="cluster-properties1" original="0">
         <nvpair id="cluster-properties1-option1" name="option1" value="value1" original="0"/>
         <nvpair id="cluster-properties1-option2" name="option2" value="value2" original="0"/>
       </cluster_property_set>
     </crm_config>
     <nodes original="1"/>
     <resources original="1">
       <primitive id="rsc1" class="ocf" provider="pacemaker" type="Dummy" original="1">
         <meta_attributes id="rsc1-meta_attributes" original="1">
           <nvpair id="rsc1-meta_attributes-option1" name="option1" value="valueX" original="1"/>
-          <nvpair id="cluster-properties1-option1" name="option1" value="value1" original="0"/>
           <nvpair id="pcmk__3_10_upgrade-cluster-properties1-option1-option3" name="option3" value="value1" original="0"/>
         </meta_attributes>
       </primitive>
       <primitive id="rsc2" class="ocf" provider="pacemaker" type="Dummy" original="1">
         <meta_attributes id="rsc2-meta_attributes" original="1">
           <nvpair id="pcmk__3_10_upgrade-cluster-properties1-option1-option3" name="option3" value="value1" original="0"/>
         </meta_attributes>
       </primitive>
     </resources>
     <constraints original="1"/>
   </configuration>
   <status original="1"/>
 </cib>
diff --git a/cts/schemas/test-3/ref/id-ref.ref-99 b/cts/schemas/test-3/ref/id-ref.ref-99
index cb4ea469b4..b088730bdd 100644
--- a/cts/schemas/test-3/ref/id-ref.ref-99
+++ b/cts/schemas/test-3/ref/id-ref.ref-99
@@ -1,66 +1,65 @@
 <cib crm_feature_set="3.19.7" validate-with="pacemaker-4.0" epoch="16" num_updates="0" admin_epoch="0">
   <configuration>
     <!-- The essential elements of this test are:
          * There is a cluster_properties_set element with an id attribute (set
            to cluster-properties1) and a set of nvpair children.
          * There are two cluster_properties_set elements with an id-ref
            attribute (set to cluster-properties1): one before and one after the
            original.
          * There is a primitive resource (rsc1) with a meta_attributes element
            containing nvpair children.
            * The first nvpair is a definition (has an id attribute).
            * The second has an id-ref attribute with no name attribute.
            * The third has id-ref="cluster-properties1-option1" and
              name="option3". Setting both id-ref and name is an undocumented
              feature that allows the same nvpair value to be used with multiple
              names (see commit 3912538 and associated pull request).
 
          In this situation:
          * In the first step of the upgrade transformation pipeline:
            * Each element with an id-ref attribute without a name attribute
              should be replaced by a copy of the element whose id attribute is
              set to the same value, but with the "original" attribute set to 1.
            * Each element with an id-ref attribute and a name attribute should
              be replaced by a copy of the element whose id attribute is set to
              the original id-ref value, except that in the copy:
              * The id attribute begins with $upgrade_prefix and ends with the
                value of @name.
              * The name attribute is overridden by the reference's @name value.
          * In the final step:
            * Resolved references that did not have name attributes should be
              converted back to references.
            * For resolved references that did have name attributes, such that
              the id of the resolved element differs from the original id-ref
              value:
              * The first element with the new id value remains expanded as a
                definition.
              * Any subsequent elements with the new id value are converted to
                references to the first one.
       -->
     <crm_config>
       <cluster_property_set id-ref="cluster-properties1"/>
       <cluster_property_set id="cluster-properties1">
         <nvpair id="cluster-properties1-option1" name="option1" value="value1"/>
         <nvpair id="cluster-properties1-option2" name="option2" value="value2"/>
       </cluster_property_set>
       <cluster_property_set id-ref="cluster-properties1"/>
     </crm_config>
     <nodes/>
     <resources>
       <primitive id="rsc1" class="ocf" provider="pacemaker" type="Dummy">
         <meta_attributes id="rsc1-meta_attributes">
           <nvpair id="rsc1-meta_attributes-option1" name="option1" value="valueX"/>
-          <nvpair id-ref="cluster-properties1-option1"/>
           <nvpair id="pcmk__3_10_upgrade-cluster-properties1-option1-option3" name="option3" value="value1"/>
         </meta_attributes>
       </primitive>
       <primitive id="rsc2" class="ocf" provider="pacemaker" type="Dummy">
         <meta_attributes id="rsc2-meta_attributes">
           <nvpair id-ref="pcmk__3_10_upgrade-cluster-properties1-option1-option3"/>
         </meta_attributes>
       </primitive>
     </resources>
     <constraints/>
   </configuration>
   <status/>
 </cib>
diff --git a/xml/upgrade-3.10-2.xsl b/xml/upgrade-3.10-2.xsl
index bafe032afb..54cec91a32 100644
--- a/xml/upgrade-3.10-2.xsl
+++ b/xml/upgrade-3.10-2.xsl
@@ -1,23 +1,98 @@
 <?xml version="1.0" encoding="UTF-8"?>
 
 <!--
  Use comments liberally as future maintainers may be unfamiliar with XSLT.
  -->
 
 <!--
  upgrade-3.10-2.xsl
 
  Guarantees after this transformation:
+ * Within a given nvset, there is at most one nvpair with a given name. If there
+   were duplicates prior to this transformation, only the first one is kept.
  -->
 
 <xsl:stylesheet version="1.0"
                 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
 
 <xsl:import href="upgrade-3.10-common.xsl"/>
 
 <!-- Copy everything unaltered by default -->
 <xsl:template match="/|@*|node()">
     <xsl:call-template name="identity"/>
 </xsl:template>
 
+
+<!-- Name/value pairs -->
+
+<!--
+ Ensure there is at most one nvpair with a given name in a given nvset.
+
+ By dropping the ignored duplicates now, we facilitate later transformations in
+ which we drop nvpairs with certain values. The later steps will involve
+ comparisons among multiple nvsets. These are easier to reason about and to
+ regression-test if, prior to that, we drop all but one nvpair with a given name
+ in a given nvset.
+ -->
+
+<!--
+ Drop nvpairs with value="#default" if there is a later nvpair with the same
+ name. Value "#default" unsets the option, so any later nvpair takes precedence.
+-->
+<xsl:template match="nvpair[(@value = '#default')
+                            and (@name = following-sibling::*/@name)]"/>
+
+<!--
+ Drop nvpairs with a value other than "#default" if certain conditions (detailed
+ below) are satisfied.
+ -->
+<xsl:template match="nvpair[@value != '#default']">
+    <!-- All preceding sibling nvpairs with the same name -->
+    <xsl:variable name="before"
+                  select="preceding-sibling::nvpair[@name = current()/@name]"/>
+
+    <!-- All following sibling nvpairs with the same name -->
+    <xsl:variable name="after"
+                  select="following-sibling::nvpair[@name = current()/@name]"/>
+
+    <!--
+     Last preceding sibling nvpair with the same name and value "#default"
+     -->
+    <xsl:variable name="last_default_before"
+                  select="$before[@value = '#default'][last()]"/>
+
+    <xsl:choose>
+        <!--
+         Drop if there's a following sibling with the same name and value
+         "#default". The later "#default" value would unset the current nvpair's
+         value.
+         -->
+        <xsl:when test="$after[@value = '#default']"/>
+
+        <!--
+         Drop if both:
+         * There's a preceding sibling nvpair with the same name
+         * Either of the following:
+           * There's no preceding sibling nvpair with the same name and value
+             "#default"
+           * There's a preceding sibling nvpair with the same name between the
+             most recent "#default" and the current node.
+
+         The preceding sibling nvpair would take effect, and there is no
+         "#default" value to unset it before we reach the current nvpair.
+
+         This uses an XPath 1.0 set intersection idiom.
+         -->
+        <xsl:when test="$before
+                        and (not($last_default_before)
+                             or $last_default_before/following-sibling::nvpair
+                                [count(.|$before) = count($before)])"/>
+
+        <!-- Otherwise, keep the nvpair -->
+        <xsl:otherwise>
+            <xsl:call-template name="identity"/>
+        </xsl:otherwise>
+    </xsl:choose>
+</xsl:template>
+
 </xsl:stylesheet>