HTML5 validation outline error: heading level skipped on the XWikiSyntaxHeadings page

Validation errors in xwiki:XWiki.XWikiSyntaxHeadings(fr)
ERROR: The heading “h3” (with computed level 3) follows the heading “h1” (with computed level 1), skipping 1 heading level. at line [1209] column [1293]
ERROR: The heading “h3” (with computed level 3) follows the heading “h1” (with computed level 1), skipping 1 heading level. at line [1216] column [878]

Extracts of the invalid content:

  1207         <div class="row">
  1208     <div id="xwikicontent" class="col-xs-12">
  1209               <h1 id="HEditing" class="wikigeneratedid"><span>Editing</span></h1><h2 id="HHeadings" class="wikigeneratedid"><span>Headings</span></h2><h3 id="H1.0Headings" class="wikigeneratedid"><span>1.0 Headings</span></h3><table><tr><th scope="col">Feature</th><th scope="col">XWiki Syntax 1.0</th><th scope="col">Result</th></tr><tr><td>Standard headings</td><td><div><p>1 level 1<br/>1.1 level 2<br/>1.1.1 level 3<br/>1.1.1.1 level 4<br/>1.1.1.1.1 level 5<br/>1.1.1.1.1.1 level 6</p></div></td><td><div><h1 id="Hlevel1" class="wikigeneratedid"><span>level 1</span></h1><p>&nbsp;</p><h2 id="Hlevel2" class="wikigeneratedid"><span>level 2</span></h2><h3 id="Hlevel3" class="wikigeneratedid"><span>level 3</span></h3><h4 id="Hlevel4" class="wikigeneratedid"><span>level 4</span></h4><h5 id="Hlevel5" class="wikigeneratedid"><span>level 5</span></h5><h6 id="Hlevel6" class="wikigeneratedid"><span>level 6</span></h6></div></td></tr><tr><td>Parameterized headings</td><td>&lt;h1&gt;&lt;span style="color:blue"&gt;Heading&lt;/span&gt;&lt;/h1&gt;</td><td><div><h1 id="Hheading" class="wikigeneratedid" style="color:blue"><span>heading</span></h1></div></td></tr><tr><td>Headings with XWiki Syntax</td><td>1.1.1 Heading with *bold*</td><td><div><h3 id="HHeadingwithbold" class="wikigeneratedid"><span>Heading with <strong>bold</strong></span></h3></div></td></tr></table><h3 id="H2.0Headings" class="wikigeneratedid"><span>2.0 Headings</span></h3><table><tr><th scope="col">Feature</th><th scope="col">XWiki Syntax $crtSyntaxVer</th><th scope="col">Result</th></tr><tr><td>Standard headings</td><td><div><pre>
  1210 = level 1 = 
  1211 == level 2 ==

  1214 ===== level 5 =====
  1215 ====== level 6 ======
  1216 </pre></div></td><td><div><h1 id="Hlevel1-1" class="wikigeneratedid"><span>level 1</span></h1><p>&nbsp;</p><h2 id="Hlevel2-1" class="wikigeneratedid"><span>level 2</span></h2><h3 id="Hlevel3-1" class="wikigeneratedid"><span>level 3</span></h3><h4 id="Hlevel4-1" class="wikigeneratedid"><span>level 4</span></h4><h5 id="Hlevel5-1" class="wikigeneratedid"><span>level 5</span></h5><h6 id="Hlevel6-1" class="wikigeneratedid"><span>level 6</span></h6></div></td></tr><tr><td>Parameterized headings</td><td><span class="wikimodel-verbatim">(% style="color:blue" %)</span><br/>= heading =</td><td><div><h1 id="Hheading-1" class="wikigeneratedid" style="color:blue"><span>heading</span></h1></div></td></tr><tr><td>Headings with XWiki Syntax</td><td><span class="wikimodel-verbatim">=== Heading with **bold** ===</span></td><td><div><h3 id="HHeadingwithbold-1" class="wikigeneratedid"><span>Heading with <strong>bold</strong></span></h3></div></td></tr></table>
  1217           </div>
  1218   </div>