mention .dropdown-backdrop and .open in dropdown docs /cc #10102

javascript.html

@@ -449,6 +449,7 @@ $('#myModal').on('hidden.bs.modal', function () {
 
 
     <h2 id="dropdowns-usage">Usage</h2>
+    <p>Via data attributes or JavaScript, the dropdown plugin toggles hidden content (dropdown menus) by toggling the <code>.open</code> class on the parent list item. When opened, the plugin also adds <code>.dropdown-backdrop</code> as a click area for closing dropdown menus when clicking outside the menu.</p>
 
     <h3>Via data attributes</h3>
     <p>Add <code>data-toggle="dropdown"</code> to a link or button to toggle a dropdown.</p>