<!-- error: /unexpected element.*parsing: <X:single_quotes/ -->
<Octothorpe xmlns:A="uri:type:A" xmlns:B="uri:type:B" xmlns:X="uri:type:X">
  <colon/>
  <A:section_mark>
    <A:section_mark>
      <interrobang/>
      <A:single_quotes/>
    </A:section_mark>
    <interrobang/>
    <X:single_quotes/>
  </A:section_mark>
</Octothorpe>