diff --git a/collection.xconf b/collection.xconf
index d7a59a51..c3850f50 100644
--- a/collection.xconf
+++ b/collection.xconf
@@ -8,6 +8,7 @@
                 <field name="author" expression="nav:get-metadata(ancestor::tei:TEI, 'author')"/>
                 <field name="language" expression="nav:get-metadata(ancestor::tei:TEI, 'language')"/>
                 <field name="date" expression="nav:get-metadata(ancestor::tei:TEI, 'date')"/>
+                <field name="category" expression="nav:get-metadata(ancestor::tei:TEI, 'category')"/>
                 <field name="file" expression="util:document-name(.)"/>
                 <field name="text" expression="."/>
                 <facet dimension="genre" expression="nav:get-metadata(ancestor::tei:TEI, 'genre')" hierarchical="yes"/>
diff --git a/data/test/DamenConvLex-1834.xml b/data/test/DamenConvLex-1834.xml
index 717ca3e5..38d2b291 100644
--- a/data/test/DamenConvLex-1834.xml
+++ b/data/test/DamenConvLex-1834.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <?teipublisher template="tei-lex.html" odd="lex-0.odd"?>
-<TEI xmlns="http://www.tei-c.org/ns/1.0" xmlns:tei="http://www.tei-c.org/ns/1.0">
+<TEI xmlns="http://www.tei-c.org/ns/1.0" n="cb">
    <teiHeader>
       <fileDesc>
          <titleStmt>
diff --git a/data/test/F-rom.xml b/data/test/F-rom.xml
index 6fd96895..6f6abb39 100644
--- a/data/test/F-rom.xml
+++ b/data/test/F-rom.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <?teipublisher template="shakespeare.html" odd="shakespeare.odd" view="page" media="pdf epub print"?>
-<TEI xmlns="http://www.tei-c.org/ns/1.0">
+<TEI xmlns="http://www.tei-c.org/ns/1.0" n="Ab">
     <teiHeader>
         <fileDesc>
             <titleStmt>
diff --git a/data/test/cortes_to_dantiscus.xml b/data/test/cortes_to_dantiscus.xml
index 2b696339..9dc47d5c 100644
--- a/data/test/cortes_to_dantiscus.xml
+++ b/data/test/cortes_to_dantiscus.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <?teipublisher template="cortez-with-translation.html" odd="dantiscus.odd" view="page" media="epub"?>
-<TEI xmlns="http://www.tei-c.org/ns/1.0" xml:id="CIDTC5772">
+<TEI xmlns="http://www.tei-c.org/ns/1.0" xml:id="CIDTC5772" n="Cc">
    <teiHeader>
       <fileDesc>
          <titleStmt>
diff --git a/data/test/cortes_to_dantiscus_Mexico.xml b/data/test/cortes_to_dantiscus_Mexico.xml
index 346fea7c..4e55c251 100644
--- a/data/test/cortes_to_dantiscus_Mexico.xml
+++ b/data/test/cortes_to_dantiscus_Mexico.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <?teipublisher template="cortez.html" odd="dantiscus.odd" view="page" media="epub"?>
-<TEI xmlns="http://www.tei-c.org/ns/1.0" xml:id="CIDTC3823">
+<TEI xmlns="http://www.tei-c.org/ns/1.0" xml:id="CIDTC3823" n="Cd">
    <teiHeader>
       <fileDesc>
          <titleStmt>
diff --git a/data/test/ebbe.xml b/data/test/ebbe.xml
index 293c8883..e4850970 100644
--- a/data/test/ebbe.xml
+++ b/data/test/ebbe.xml
@@ -1,7 +1,7 @@
 <?xml-model href="http://www.tei-c.org/release/xml/tei/custom/schema/relaxng/tei_all.rng" type="application/xml" schematypens="http://relaxng.org/ns/structure/1.0"?><?xml-model href="http://www.tei-c.org/release/xml/tei/custom/schema/relaxng/tei_all.rng" type="application/xml"
 	schematypens="http://purl.oclc.org/dsdl/schematron"?>
 <?teipublisher template="ebbe.html" odd="ebbe.odd" view="page" media="epub"?>
-<TEI xmlns="http://www.tei-c.org/ns/1.0" xml:id="EBBE_BS_sample">
+<TEI xmlns="http://www.tei-c.org/ns/1.0" xml:id="EBBE_BS_sample" n="Ce">
    <teiHeader>
       <fileDesc>
          <titleStmt>
diff --git a/data/test/graves6.xml b/data/test/graves6.xml
index 1e7fcbda..f5923c69 100644
--- a/data/test/graves6.xml
+++ b/data/test/graves6.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <?teipublisher odd="graves.odd" template="letter.html" media="latex epub print fo"?>
-<TEI xmlns="http://www.tei-c.org/ns/1.0" xmlns:xi="http://www.w3.org/2001/XInclude">
+<TEI xmlns="http://www.tei-c.org/ns/1.0" xmlns:xi="http://www.w3.org/2001/XInclude" n="Ac">
     <teiHeader>
         <fileDesc>
             <titleStmt>
diff --git a/data/test/kant_rvernunft_1781.TEI-P5.xml b/data/test/kant_rvernunft_1781.TEI-P5.xml
index 1e090747..a10f15da 100644
--- a/data/test/kant_rvernunft_1781.TEI-P5.xml
+++ b/data/test/kant_rvernunft_1781.TEI-P5.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?><?oxygen RNGSchema="http://www.deutschestextarchiv.de/basisformat.rng" type="xml"?>
 <?teipublisher view="page" odd="dta.odd" template="dta.html" media="epub print"?>
-<TEI xmlns="http://www.tei-c.org/ns/1.0">
+<TEI xmlns="http://www.tei-c.org/ns/1.0" n="Aa">
     <teiHeader>
         <fileDesc>
             <titleStmt>
diff --git a/data/test/let695.xml b/data/test/let695.xml
index 64107b43..094b8793 100644
--- a/data/test/let695.xml
+++ b/data/test/let695.xml
@@ -3,7 +3,7 @@
 <!--Licensed under Attribution-NonCommercial-ShareAlike 4.0 International (CC BY-NC-SA 4.0)-->
 <?xml-model href="https://xmlschema.huygens.knaw.nl/vgodd.rng" type="application/xml" schematypens="http://relaxng.org/ns/structure/1.0"?>
 <?teipublisher odd="vangogh.odd" template="vangogh.html" view="page" media="latex"?>
-<TEI xmlns:vg="http://www.vangoghletters.org/ns/" xmlns="http://www.tei-c.org/ns/1.0">
+<TEI xmlns:vg="http://www.vangoghletters.org/ns/" xmlns="http://www.tei-c.org/ns/1.0" n="Ca">
   <teiHeader xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
     <fileDesc>
       <titleStmt>
diff --git a/data/test/orlik_to_serafin.xml b/data/test/orlik_to_serafin.xml
index d62fc8d1..0bcfaa88 100644
--- a/data/test/orlik_to_serafin.xml
+++ b/data/test/orlik_to_serafin.xml
@@ -1,5 +1,5 @@
 <?teipublisher template="translation.html" odd="serafin.odd" view="div" media="print latex epub"?>
-<TEI xmlns="http://www.tei-c.org/ns/1.0" xml:id="MS2">
+<TEI xmlns="http://www.tei-c.org/ns/1.0" xml:id="MS2" n="Bb">
    <teiHeader>
       <fileDesc>
          <titleStmt>
diff --git a/data/test/osinski.xml b/data/test/osinski.xml
index 9c51e917..7b6a213c 100644
--- a/data/test/osinski.xml
+++ b/data/test/osinski.xml
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <?teipublisher template="osinski.html" odd="osinski.odd" view="page" media="epub print"?>
-<TEI xmlns="http://www.tei-c.org/ns/1.0">
+<TEI xmlns="http://www.tei-c.org/ns/1.0" n="Ca">
    <teiHeader>
       <fileDesc>
          <titleStmt>
diff --git a/data/test/pb-mei-app.xml b/data/test/pb-mei-app.xml
index 04b9c06f..40baffb7 100644
--- a/data/test/pb-mei-app.xml
+++ b/data/test/pb-mei-app.xml
@@ -2,7 +2,7 @@
 <?teipublisher media="print" template="mei.html"?>
 <?xml-model href="bolz_example.rng" type="application/xml" schematypens="http://relaxng.org/ns/structure/1.0"?>
 <?xml-model href="bolz_example.rng" type="application/xml" schematypens="http://purl.oclc.org/dsdl/schematron"?>
-<TEI xmlns="http://www.tei-c.org/ns/1.0">
+<TEI xmlns="http://www.tei-c.org/ns/1.0" n="Ad">
 	<teiHeader>
 		<fileDesc>
 			<titleStmt>
diff --git a/data/test/test.docx.xml b/data/test/test.docx.xml
index 9fd66188..1ce20174 100644
--- a/data/test/test.docx.xml
+++ b/data/test/test.docx.xml
@@ -1,5 +1,5 @@
 <?teipublisher odd="docx-output.odd"?>
-<TEI xmlns="http://www.tei-c.org/ns/1.0">
+<TEI xmlns="http://www.tei-c.org/ns/1.0" n="Ba">
     <teiHeader>
         <fileDesc>
             <titleStmt>
diff --git a/index.xql b/index.xql
index 0d56f93a..0cf8d8d0 100644
--- a/index.xql
+++ b/index.xql
@@ -60,6 +60,8 @@ declare function idx:get-metadata($root as element(), $field as xs:string) {
                 root($root)//dbk:info/dbk:keywordset[@vocab="#genre"]/dbk:keyword,
                 root($root)//article-meta/kwd-group[@kwd-group-type="genre"]/kwd
             )
+            case "category" return
+                (root($root)/tei:TEI/@n, "ZZZ")[1]
             case "feature" return (
                 idx:get-classification($header, 'feature'),
                 $root/dbk:info/dbk:keywordset[@vocab="#feature"]/dbk:keyword
@@ -94,4 +96,4 @@ declare function idx:get-classification($header as element()?, $scheme as xs:str
     let $category := id(substring($target, 2), doc($idx:app-root || "/data/taxonomy.xml"))
     return
         $category/ancestor-or-self::tei:category[parent::tei:category]/tei:catDesc
-};
+};
\ No newline at end of file
diff --git a/modules/lib/browse.xql b/modules/lib/browse.xql
index ef54d982..bc6ce003 100644
--- a/modules/lib/browse.xql
+++ b/modules/lib/browse.xql
@@ -56,7 +56,7 @@ function app:clear-facets($node as node(), $model as map(*)) {
 declare 
     %templates:wrap
     %templates:default("field", "text")
-    %templates:default("sort", "title")
+    %templates:default("sort", "category")
 function app:form($node as node(), $model as map(*), $field as xs:string, $sort as xs:string) {
     map {
         "field": $field,
diff --git a/templates/index.html b/templates/index.html
index 23db809e..0b1a0b9a 100644
--- a/templates/index.html
+++ b/templates/index.html
@@ -90,6 +90,7 @@ <h1 class="tp-title">The Instant Publishing Toolbox<small data-template="pages:v
                                             <pb-custom-form class="options">
                                                 <input type="hidden" name="collection" value="${collection}" data-template="pages:parse-params"/>
                                                 <pb-select label="browse.sort" name="sort" value="${sort}" data-template="pages:parse-params">
+                                                    <paper-item value="category"><pb-i18n key="browse.category">Default</pb-i18n></paper-item>
                                                     <paper-item value="title"><pb-i18n key="browse.title"></pb-i18n></paper-item>
                                                     <paper-item value="author"><pb-i18n key="browse.author"></pb-i18n></paper-item>
                                                 </pb-select>