Issue: implicit grouping in <start>

Currently

<start>
  <ref name="foo"/>
  <ref name="bar"/>
</start>

means

<start>
  <group>
    <ref name="foo"/>
    <ref name="bar"/>
  </group>
</start>

Would it be better for this to be an error or for it to mean

<start>
  <choice>
    <ref name="foo"/>
    <ref name="bar"/>
  </choice>
</start>

?

James