Add external hooks to now {visible,hidden} algorithms

index.html

@@ -339,6 +339,8 @@ <h2>
           bubbles, isn't cancelable, and has no default action, at the
           <var>doc</var>.
         </li>
+        <li>Run <dfn>external now visible algorithm</dfn> if one is defined by
+        another specification.</li>
       </ol>
       <p>
         The <dfn>now hidden algorithm</dfn> runs the following steps
@@ -353,6 +355,8 @@ <h2>
           bubbles, isn't cancelable, and has no default action, at the
           <var>doc</var>.
         </li>
+        <li>Run <dfn>external now hidden algorithm</dfn> if one is defined by
+        another specification.</li>
       </ol>
     </section>
     <section id="privacy-security">