<sdf version='1.7'>
  <model name="top" canonical_link="nested::link">
    <model name="nested">
      <link name="link"/>
    </model>
    <model name="nested_without_links1">
      <model name="nested_without_links2">
        <model name="nested_without_links3">
          <frame name="F"/>
        </model>
      </model>
    </model>
  </model>
</sdf>
