Update eventListeners.rst

how-to/eventListeners.rst

@@ -7,8 +7,8 @@ WebExtensions can react on events by attaching a listener. Consider the :ref:`me
 .. code-block:: javascript
 
   async function menuListener(info, tab) {
-    ...
-    // do something with the info and tab parameters received from the event
+    // Do something with the info and tab parameters
+    // received from the event.
   }
   
   messenger.menus.onClicked.addListener(menuListener);
@@ -18,6 +18,23 @@ Alternative implementation using an anonymous arrow function:
 .. code-block:: javascript
  
   messenger.menus.onClicked.addListener(async (info, tab) => {
-    // do something with the info and tab parameters received from the event
-	...
+    // Do something with the info and tab parameters
+    // received from the event.
   });
+
+Events with additional parameters
+=================================
+
+Some events support additional parameters, for example the :ref:`messages.onNewMailReceived` event.
+
+The additional parameter ``monitorAllFolders`` is the second parameter of the ``addListener``
+function, specifying whether to monitor just the standard inbox folders, or all folders.
+
+.. code-block:: javascript
+
+  async function listener(folder, messages) {
+    // Do something with the folder and messages parameters
+    // received from the event.
+  }
+  
+  messenger.messages.onNewMailReceived.addListener(listener, true);