Named Object Abstract Nested

In XMIR, named objects cannot be nested deeper than one level inside an abstract object.

Incorrect:

<objects>
  <o base="x" name="@">
    <o base="y" name="a">
      <o base="z" name="b"/>
    </o>
  </o>
</objects>

Correct:

<objects>
  <o base="x" name="@">
    <o base="$.a"/>
  </o>
  <o base="y" name="a">
    <o base="$.b"/>
  </o>
  <o base="z" name="b"/>
</objects>