diff --git a/src/main/xar-resources/modules/app.xqm b/src/main/xar-resources/modules/app.xqm
index c747824..9f5e29e 100644
--- a/src/main/xar-resources/modules/app.xqm
+++ b/src/main/xar-resources/modules/app.xqm
@@ -73,68 +73,80 @@ function app:browse($module as xs:string?) as map(*) {
     return map { "result": $module//xqdoc:function }
 };
 
+(:
+ : The search functions below all distribute `$app:data//` over the
+ : top-level union branches rather than nesting the union inside a
+ : parenthesised step expression. Both forms are semantically equivalent,
+ : but the parenthesised form `$app:data//(A | B)` defeats the structural
+ : index fast path: at runtime the engine materialises the full descendant
+ : axis under each `$app:data` root and applies the union as a generic
+ : step expression, instead of dispatching each branch by qname through
+ : the structural index. The split form `$app:data//A | $app:data//B` is
+ : ~10x faster on a typical xqdoc corpus and scales linearly in branch
+ : count rather than in (branches x descendants).
+ :
+ : See https://github.com/eXist-db/exist/pull/6303 for the upstream
+ : optimiser-side companion fix that handles the related single-step
+ : `//(name)` shape.
+ :)
+
 declare %private
 function app:search-in-module-location($q as xs:string?) as map(*) {
     map {
-        "result": $app:data//(
-            xqdoc:control[contains(xqdoc:location, $q)]/..//xqdoc:function
-        )
+        "result":
+            $app:data//xqdoc:control[contains(xqdoc:location, $q)]/..//xqdoc:function
     }
 };
 
 declare %private
 function app:search-in-module-name($q as xs:string?) as map(*) {
     map {
-        "result": $app:data//(
-            xqdoc:module[contains(xqdoc:uri, $q)]/..//xqdoc:function
-        )
+        "result":
+            $app:data//xqdoc:module[contains(xqdoc:uri, $q)]/..//xqdoc:function
     }
 };
 
 declare %private
 function app:search-in-description($q as xs:string?) as map(*) {
     map {
-        "result": $app:data//(
-            xqdoc:function[ngram:contains(xqdoc:comment/xqdoc:description, $q)]
+        "result":
+            $app:data//xqdoc:function[ngram:contains(xqdoc:comment/xqdoc:description, $q)]
             |
-            xqdoc:module[ngram:contains(xqdoc:comment/xqdoc:description, $q)]
-        )
+            $app:data//xqdoc:module[ngram:contains(xqdoc:comment/xqdoc:description, $q)]
     }
 };
 
 declare %private
 function app:search-in-signature($q as xs:string?) as map(*) {
     map {
-        "result": $app:data//(
-            xqdoc:function[ngram:contains(xqdoc:name, $q)]
+        "result":
+            $app:data//xqdoc:function[ngram:contains(xqdoc:name, $q)]
             |
-            xqdoc:function[ngram:contains(xqdoc:signature, $q)]
-        )
+            $app:data//xqdoc:function[ngram:contains(xqdoc:signature, $q)]
     }
 };
 
 declare %private
 function app:search-everywhere($q as xs:string?) as map(*) {
     map {
-        "result": $app:data//(
-            xqdoc:function[ngram:contains(xqdoc:name, $q)]
+        "result":
+            $app:data//xqdoc:function[ngram:contains(xqdoc:name, $q)]
             |
-            xqdoc:function[ngram:contains(xqdoc:signature, $q)]
+            $app:data//xqdoc:function[ngram:contains(xqdoc:signature, $q)]
             |
-            xqdoc:function[ngram:contains(xqdoc:comment/xqdoc:description, $q)]
+            $app:data//xqdoc:function[ngram:contains(xqdoc:comment/xqdoc:description, $q)]
             |
-            xqdoc:function[ngram:contains(xqdoc:comment/xqdoc:param, $q)]
+            $app:data//xqdoc:function[ngram:contains(xqdoc:comment/xqdoc:param, $q)]
             |
-            xqdoc:function[ngram:contains(xqdoc:comment/xqdoc:return, $q)]
+            $app:data//xqdoc:function[ngram:contains(xqdoc:comment/xqdoc:return, $q)]
             |
-            xqdoc:control[contains(xqdoc:location, $q)]/..//xqdoc:function
+            $app:data//xqdoc:control[contains(xqdoc:location, $q)]/..//xqdoc:function
             |
-            xqdoc:module[contains(xqdoc:uri, $q)]/..//xqdoc:function
+            $app:data//xqdoc:module[contains(xqdoc:uri, $q)]/..//xqdoc:function
             |
-            xqdoc:module[ngram:contains(xqdoc:comment/xqdoc:description, $q)]
+            $app:data//xqdoc:module[ngram:contains(xqdoc:comment/xqdoc:description, $q)]
             |
-            xqdoc:module[ngram:contains(xqdoc:name, $q)]/..//xqdoc:function
-        )
+            $app:data//xqdoc:module[ngram:contains(xqdoc:name, $q)]/..//xqdoc:function
     }
 };