HTML5 validation outline error: heading level skipped on the entityNameValidation administration page

Validation errors in xwiki:XWiki.EntityNameValidation.Administration()
ERROR: The heading “h3” (with computed level 3) follows the heading “h1” (with computed level 1), skipping 1 heading level. at line [1264] column [4]

Extracts of the invalid content:

  1262 </dl>
  1263 <div id="character-replacement-options" class="hidden">
  1264 <h3>Character Replacement Strategy Configuration</h3>
  1265                                                                                                                                                                                                                                                                 <div class="xwiki-livetable-container">
  1266           <table id="replacementCharacters" class="xwiki-livetable"