Plugin: add render_feed hook and call it while generating ATOM and RSS feed.

Create an example of the new hook in the demo plugin.

plugins/demo_plugin/demo_plugin.php

@@ -322,4 +322,29 @@ function hook_demo_plugin_delete_link($data)
     if (strpos($data['url'], 'youtube.com') !== false) {
         exit('You can not delete a YouTube link. Don\'t ask.');
     }
-}
+}
+
+/**
+ * Execute render_feed hook.
+ * Called with ATOM and RSS feed.
+ *
+ * Special data keys:
+ *   - _PAGE_: current page
+ *   - _LOGGEDIN_: true/false
+ *
+ * @param array $data data passed to plugin
+ *
+ * @return array altered $data.
+ */
+function hook_demo_plugin_render_feed($data)
+{
+    foreach ($data['links'] as &$link) {
+        if ($data['_PAGE_'] == Router::$PAGE_FEED_ATOM) {
+            $link['description'] .= ' - ATOM Feed' ;
+        }
+        elseif ($data['_PAGE_'] == Router::$PAGE_FEED_RSS) {
+            $link['description'] .= ' - RSS Feed';
+        }
+    }
+    return $data;
+}