DOMDocument::Serialize, which is called by Drupal's Html::normalize before Drupal 10, appears to fix mismatching tags, but HTML5-php does not.
With DOMDocument, Html::normalize() on <h3>Heading</h2> is giving <h3>Heading</h3>.
With HTL5-php, Html::normalize() on <h3>Heading</h2> is giving <h3>Heading</p>.
Arguably not a bug, though it has caused a regression in one use case (https://www.drupal.org/project/toc_api/issues/3416816)
DOMDocument::Serialize, which is called by Drupal's Html::normalize before Drupal 10, appears to fix mismatching tags, but HTML5-php does not.With DOMDocument,
Html::normalize()on<h3>Heading</h2>is giving<h3>Heading</h3>.With HTL5-php,
Html::normalize()on<h3>Heading</h2>is giving<h3>Heading</p>.Arguably not a bug, though it has caused a regression in one use case (https://www.drupal.org/project/toc_api/issues/3416816)