Remove secondary browsing contexts (<link rel="sidebar">)

Fixes #582.

source

@@ -20830,11 +20830,6 @@ interface <dfn>HTMLHyperlinkElementUtils</dfn> {
     the <code data-x="attr-hyperlink-target">target</code> attribute as the browsing context name. If
     these rules result in the creation of a new <span>browsing context</span>, set <var>replace</var> to true.</p>
 
-    <p>Otherwise, if the hyperlink is a <span data-x="rel-sidebar-hyperlink">sidebar
-    hyperlink</span>, the user agent implements a feature that can be considered a <span>secondary
-    browsing context</span>, and the user agent intends to use this feature in this instance, let
-    <var>target</var> be such a <span>secondary browsing context</span>.</p>
-
     <p>Otherwise, if <var>target</var> is an <code>a</code> or <code>area</code> element
     with no <code data-x="attr-hyperlink-target">target</code> attribute, but the
     <code>Document</code> contains a <code>base</code> element with a <code
@@ -21379,13 +21374,6 @@ interface <dfn>HTMLHyperlinkElementUtils</dfn> {
      <td>Gives a link to a resource that can be used to search through the current document and its related pages.</td>
     </tr>
 
-    <tr>
-     <td><code data-x="rel-sidebar">sidebar</code></td> <!-- used quite a bit -->
-     <td><span>Hyperlink</span></td>
-     <td><span>Hyperlink</span></td>
-     <td>Specifies that the referenced document, if retrieved, is intended to be shown in the browser's sidebar (if it has one).</td>
-    </tr>
-
     <tr>
      <td><code data-x="rel-stylesheet">stylesheet</code></td> <!-- most commonly used <link rel> value, variants came in 7th, 8th, 12th, 17th... -->
      <td><span data-x="external resource link">External Resource</span></td>
@@ -21925,19 +21913,6 @@ interface <dfn>HTMLHyperlinkElementUtils</dfn> {
   interfaces. <ref spec=OPENSEARCH></p>
 
 
-  <h5>Link type "<dfn><code data-x="rel-sidebar">sidebar</code></dfn>"</h5>
-
-  <p>The <code data-x="rel-sidebar">sidebar</code> keyword may be used with <code>link</code>,
-  <code>a</code>, and <code>area</code> elements. This keyword creates a <span>hyperlink</span>.</p>
-
-  <p>The <code data-x="rel-sidebar">sidebar</code> keyword indicates that the referenced document, if
-  retrieved, is intended to be shown in a <span>secondary browsing context</span> (if possible),
-  instead of in the current <span>browsing context</span>.</p>
-
-  <p>A <span>hyperlink</span> with the <code data-x="rel-sidebar">sidebar</code> keyword specified is
-  a <dfn data-x="rel-sidebar-hyperlink">sidebar hyperlink</dfn>.</p>
-
-
 <!--ADD-TOPIC:CSS-->
   <h5>Link type "<dfn><code data-x="rel-stylesheet">stylesheet</code></dfn>"</h5>
 
@@ -76097,16 +76072,6 @@ dictionary <dfn>DragEventInit</dfn> : <span>MouseEventInit</span> {
 
 
 
-  <h4>Secondary browsing contexts</h4>
-
-  <p>User agents may support <dfn data-x="secondary browsing context">secondary browsing
-  contexts</dfn>, which are <span data-x="browsing context">browsing contexts</span> that form part
-  of the user agent's interface, apart from the main content area.</p>
-
-  <p class="note">The <code data-x="rel-sidebar">sidebar</code> link type uses <span data-x="secondary
-  browsing context">secondary browsing contexts</span>.</p>
-
-
 <!--ADD-TOPIC:Security-->
   <div w-nodev>