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

javascript.html

@@ -232,6 +232,7 @@ <h4>Make modals accessible</h4>
     </div>
 
     <h2 id="modals-usage">Usage</h2>
+    <p>The modal plugin toggles your hidden content on demand, via data attributes or JavaScript. It also adds <code>.model-open</code> to the <code>&lt;body&gt;</code> to override default scrolling behavior and generates a <code>.modal-backdrop</code> to provide a click area for dismissing shown modals when clicking outside the modal.</p>
 
     <h3>Via data attributes</h3>
     <p>Activate a modal without writing JavaScript. Set <code>data-toggle="modal"</code> on a controller element, like a button, along with a <code>data-target="#foo"</code> or <code>href="#foo"</code> to target a specific modal to toggle.</p>