QtWebengine does not follow the w3c editing spec

void InsertParagraphSeparatorCommand::ApplyStyleAfterInsertion(
    Element* original_enclosing_block,
    EditingState* editing_state) {
  // Not only do we break out of header tags, but we also do not preserve the
  // typing style, in order to match other browsers.
  if (original_enclosing_block->HasTagName(h1Tag) ||
      original_enclosing_block->HasTagName(h2Tag) ||
      original_enclosing_block->HasTagName(h3Tag) ||
      original_enclosing_block->HasTagName(h4Tag) ||
      original_enclosing_block->HasTagName(h5Tag)) {
    return;
  }

...

bool InsertParagraphSeparatorCommand::ShouldUseDefaultParagraphElement(
    Element* enclosing_block) const {
  DCHECK(!GetDocument().NeedsLayoutTreeUpdate());

  if (must_use_default_paragraph_element_)
    return true;

  // Assumes that if there was a range selection, it was already deleted.
  if (!IsEndOfBlock(EndingVisibleSelection().VisibleStart()))
    return false;

  return enclosing_block->HasTagName(h1Tag) ||
         enclosing_block->HasTagName(h2Tag) ||
         enclosing_block->HasTagName(h3Tag) ||
         enclosing_block->HasTagName(h4Tag) ||
         enclosing_block->HasTagName(h5Tag);
}