Document optional unified search result entry attributes

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>

developer_manual/app_publishing_maintenance/upgrade-guide.rst

@@ -40,7 +40,7 @@ jQuery was updated to v2.2. The most notable change is that ``$(document).ready(
 Search
 ******
 
-The unified search replaces the traditional search input, hence ``OCA.Search`` became a noop. For backwards compatibility, the code will not raise any errors now, but it does not have any functionality.
+The :ref:`unified search<unified-search>` replaces the traditional search input, hence ``OCA.Search`` became a noop. For backwards compatibility, the code will not raise any errors now, but it does not have any functionality.
 
 Removed globals
 ***************

developer_manual/digging_deeper/search.rst

@@ -1,3 +1,5 @@
+.. _unified-search:
+
 ======
 Search
 ======
@@ -394,3 +396,19 @@ For a **cursor-based pagination** a app-specific property is used to know a refe
             );
         }
     }
+
+Optional attributes
+^^^^^^^^^^^^^^^^^^^
+
+The unified search is available via OCS, which means client application like the mobile apps can use it to get access to the server search mechanism. The default properties of a search result entry might be difficult to parse and interpret in those clients, hence it's possible to add optional string attributes to each entry.
+
+.. code-block:: php
+
+    <?php
+
+    $entry = new SearchResultEntry(/* same arguments as above */);
+    $entry->addAttribute("type", "deckCard");
+    $entry->addAttribute("cardId", "1234");
+    $entry->addAttribute("boardId", "567");
+
+.. note:: This method was added in Nextcloud 21. If your app also targets Nextcloud 20 you should either not use it or add a version check to invoke the method only conditionally.