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

Validation errors in xwiki:XWiki.XWikiSyntax()
ERROR: The heading “h3” (with computed level 3) follows the heading “h1” (with computed level 1), skipping 1 heading level. at line [1230] column [1038]
ERROR: The heading “h3” (with computed level 3) follows the heading “h1” (with computed level 1), skipping 1 heading level. at line [1377] column [212]

Extracts of the invalid content:

  1228 ===== level 5 =====
  1229 ====== level 6 ======
  1230 </pre></div></td><td><div><h1 id="Hlevel1-1" class="wikigeneratedid wikigeneratedheader"><span>level 1</span></h1><p>&nbsp;</p><h2 id="Hlevel2-1" class="wikigeneratedid wikigeneratedheader"><span>level 2</span></h2><h3 id="Hlevel3-1" class="wikigeneratedid wikigeneratedheader"><span>level 3</span></h3><h4 id="Hlevel4-1" class="wikigeneratedid wikigeneratedheader"><span>level 4</span></h4><h5 id="Hlevel5-1" class="wikigeneratedid wikigeneratedheader"><span>level 5</span></h5><h6 id="Hlevel6-1" class="wikigeneratedid wikigeneratedheader"><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 wikigeneratedheader" 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 wikigeneratedheader"><span>Heading with <strong>bold</strong></span></h3></div></td></tr></table><h3 id="HTextFormatting" class="sectionheader wikigeneratedheader"><span>Text Formatting</span></h3><h3 id="H2.0TextFormatting" class="wikigeneratedid wikigeneratedheader"><span>2.0 Text Formatting</span></h3><table><tr><th scope="col">Feature</th><th scope="col">XWiki Syntax 2.1</th><th scope="col">Result</th></tr><tr><td>Bold</td><td><span class="wikimodel-verbatim">**bold**</span></td><td><strong>bold</strong></td></tr><tr><td>Underline</td><td><span class="wikimodel-verbatim">__underline__</span></td><td><ins>underline</ins></td></tr><tr><td>Italics</td><td><span class="wikimodel-verbatim">//italic//</span></td><td><em>italic</em></td></tr><tr><td>Striked out</td><td><span class="wikimodel-verbatim">--strike--</span></td><td><del>strike</del></td></tr><tr><td>Monospace</td><td><span class="wikimodel-verbatim">##monospace##</span></td><td><span class="monospace">monospace</span></td></tr><tr><td>Superscript</td><td><span class="wikimodel-verbatim">some ^^superscript^^</span></td><td>some <sup>superscript</sup></td></tr><tr><td>Subscript</td><td><span class="wikimodel-verbatim">some ,,subscript,,</span></td><td>some <sub>subscript</sub></td></tr></table><h3 id="HHorizontalLine" class="sectionheader wikigeneratedheader"><span>Horizontal Line</span></h3><h3 id="H2.0HorizontalLine" class="wikigeneratedid wikigeneratedheader"><span>2.0 Horizontal Line</span></h3><div class="box infomessage"><span class="icon-block"><span class="fa fa-info-circle" aria-hidden="true"></span></span><span class="sr-only">Information</span><div><p>There must be 4 or more dashes.</p></div></div><table><tr><th scope="col">Feature</th><th scope="col">XWiki Syntax 2.1</th><th scope="col">Result</th></tr><tr><td>Simple horizontal line</td><td><span class="wikimodel-verbatim">----</span></td><td><div><hr/></div></td></tr><tr><td>Parametrized horizontal line</td><td><div><pre>
  1231 (% style="border-color:blue" %)
  1232 ----

  1375 </pre></div></td><td><div><table><tr><th scope="col">Header 1</th><th scope="col">Header 2</th><th scope="col">Header 3</th></tr><tr><td>Cell One</td><td><div><h1 id="HEmbeddeddocument"><span>Embedded document</span></h1><p>Some embedded paragraph.</p><ul><li>list item one</li><li>list item two<ul><li>sub-item 1</li><li>sub-item 2</li></ul></li></ul></div></td><td>&nbsp;Cell Three</td></tr></table><p>Next paragraph in the top-level document</p></div></td></tr><tr><td><div><pre>(% class="myClass" style="color:blue" %)(((blue paragraphs
  1376 
  1377 inside myClass)))</pre></div></td><td>&nbsp;<div class="myClass" style="color:blue"><p>blue paragraphs</p><p>inside my group</p></div></td></tr></table><h3 id="HEscapes" class="sectionheader wikigeneratedheader"><span>Escapes</span></h3><h3 id="H2.0Escapes" class="wikigeneratedid wikigeneratedheader"><span>2.0 Escapes</span></h3><p>Allows to escape XWiki Syntax.</p><table><tr><th scope="col">Feature</th><th scope="col">XWiki Syntax 2.1</th><th scope="col">Result</th></tr><tr><td>Escape a character</td><td><div><p><span class="wikimodel-verbatim">This is not a ~[~[link~]~]</span><br/><span class="box infomessage"><span class="icon-block"><span class="fa fa-info-circle" aria-hidden="true"></span></span><span class="sr-only">Information</span>To enter a ~ character use a double escape: ~~</span></p></div></td><td><span class="wikimodel-verbatim">This is not a [[link]]</span></td></tr><tr><td>Escape longer text<br/>(also see "Verbatim")</td><td>&#123;&#123;&#123;<span class="wikimodel-verbatim"> some **longer** text //without// formatting</span>}}}</td><td><span class="wikimodel-verbatim"> some **longer** text //without// formatting</span></td></tr></table><h3 id="HParameters" class="sectionheader wikigeneratedheader"><span>Parameters</span></h3><h3 id="H2.0Parameters" class="wikigeneratedid wikigeneratedheader"><span>2.0 Parameters</span></h3><p>With XWiki Syntax 2.1 it's possible to pass parameters to the different syntax elements and also to blocks of text. This is used for example to style them. You can set any parameter key/value pair you want. The XHTML renderer will pass these parameters as XHTML attributes to the underlying XHTML representation of the different syntax elements.</p><table><tr><th style="width:60%" scope="col">XWiki Syntax 2.1</th><th scope="col">Generated XHTML</th></tr><tr><td><div><pre>
  1378 (% class="myClass" style="myStyle" id="myId" %)
  1379 = heading =

Validation errors in xwiki:XWiki.XWikiSyntaxHeadings()
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>