Update index.html

Author: LanWei22

index.html

@@ -7015,6 +7015,22 @@ <h4 id=input-sources>Sources</h4>
  </tr>
 </table>
 
+<p>A <dfn>wheel input source</dfn> is an <a>input source</a>
+ that is associated with a wheel-type input device.
+ A <a>wheel input source</a> supports the same <a>pause</a> action
+ as a <a>null input source</a> plus the following actions:
+
+ <table class=simple>
+  <tr>
+   <th>Action
+   <th>Non-normative Description
+  </tr>
+  <tr>
+   <td><dfn>scroll</dfn></td>
+   <td>Used to indicate that the scroll wheel is rolled down, up, right
+    or left to scroll the page down, up, right or left.</td>
+  </tr>
+ </table>
 <p>Each <a>session</a> maintains a <a>list</a> of <dfn>active input
 sources</dfn>. This list is initially empty. When an <a>input
 source</a> is added to the list of <a>active input sources</a>, a