Vibration API Recommendation errata

These non-normative changes align the Vibration API spec with the
latest Page Visibility API spec by tapping into its hooks defined
post-Vibration API Recommendation publication:

- determine if the document is hidden
- visibility states

In addition, terminology is clarified as follows:

- browsing context -> top-level browsing context

index.html

@@ -105,8 +105,8 @@ <h2>
       </h2>
       <p>
         The concepts <dfn><a href=
-        "http://www.w3.org/TR/html5/browsers.html#browsing-context">browsing
-        context</a></dfn> and <dfn><a href=
+        "https://www.w3.org/TR/html5/browsers.html#top-level-browsing-context">top-level
+        browsing context</a></dfn> and <dfn><a href=
         "http://www.w3.org/TR/html5/webappapis.html#spin-the-event-loop">spin
         the event loop</a></dfn> are defined in [[!HTML5]].
       </p>
@@ -149,10 +149,10 @@ <h2>
         <li>Let <var>valid pattern</var> be the result of passing
         <var>pattern</var> to <a>validate and normalize</a>.
         </li>
-        <li>If the <code><a href=
-        "http://dvcs.w3.org/hg/webperf/raw-file/tip/specs/PageVisibility/Overview.html#dom-document-hidden">
-          hidden</a></code> attribute [[!PAGE-VISIBILITY]] is set to true, then
-          return false and terminate these steps.
+        <li>If the result of running the steps to <a href=
+        "https://w3c.github.io/page-visibility/#dfn-steps-to-determine-if-the-document-is-hidden">
+          determine if the document is hidden</a> [[!PAGE-VISIBILITY]] is true,
+          then return false and terminate these steps.
           <div class="note">
             A trusted (also known as privileged) application that integrates
             closely with the operating system's functionality may vibrate the
@@ -222,11 +222,12 @@ <h2>
       <ol>
         <li>An implementation MAY return false and terminate these steps.
           <div class="note">
-            For example, an implementation might abort the algorithm because
-            the user has set a preference indicating that pages at a given
-            origin should never be able to vibrate the device, or an
-            implementation might cap the total amount of time a page may cause
-            the device to vibrate and reject requests in excess of this limit.
+            For example, an implementation might abort the algorithm because no
+            vibration hardware is present, the user has set a preference
+            indicating that pages at a given origin should never be able to
+            vibrate the device, or an implementation might cap the total amount
+            of time a page may cause the device to vibrate and reject requests
+            in excess of this limit.
           </div>
         </li>
         <li>If another instance of the <a>perform vibration</a> algorithm is
@@ -255,12 +256,11 @@ <h2>
         </li>
       </ol>
       <p>
-        When the <code><a href=
-        "http://dvcs.w3.org/hg/webperf/raw-file/tip/specs/PageVisibility/Overview.html#sec-visibilitychange-event">
-        visibilitychange</a></code> event [[!PAGE-VISIBILITY]] is dispatched at
-        the <code>Document</code> in a <a>browsing context</a>, the <a class=
-        "product-ua" href="#ua">user agent</a> MUST abort the already running
-        <a>processing vibration patterns</a> algorithm, if any.
+        When the user agent determines that the <a href=
+        "https://w3c.github.io/page-visibility/#dfn-visibility-states">visibility
+        state</a> of the <code>Document</code> of the <a>top-level browsing
+        context</a> changes, it MUST abort the already running <a>processing
+        vibration patterns</a> algorithm, if any.
       </p>
     </section>
     <section class='informative'>