add special mods identifier for sort IDs

src/main/resources/xsl/biocol2solr.xsl

@@ -23,6 +23,15 @@
       <field name="mods.identifier">
         <xsl:value-of select="./metadata/def.biocol01/biocol01/text()" />
       </field>
+      <field name="mods.identifier.unique.sortable">
+        <xsl:value-of select="./@label" />
+      </field>
+      <field name="mods.identifier.unique.string">
+        <xsl:value-of select="./metadata/def.biocol01/biocol01/text()" />
+      </field>
+      <field name="mods.identifier.unique.splited">
+        <xsl:value-of select="./metadata/def.biocol01/biocol01/text()" />
+      </field>
     </xsl:if>
 
     <xsl:if test="./metadata/def.biocol05/biocol05">