<?xml version="1.0" ?>
<sdf version='1.7' xmlns:test="http://example.org/schema">
  <world name="default">
    <model name="M">
      <link name="link"/>
      <test:custom_elem>
        <link name="L"/>
        <link name="L"/>
      </test:custom_elem>
    </model>
  </world>
</sdf>
