How do you reference another element in a xaml list

Question

I'm using xaml as a datastore because It's quick and we haven't yet defined a file format. But I can only seem to create xaml that is a pure tree, even if it is acyclic.

I know how to create a list of items in xaml, but How do I share objects in two lists? Below is an example of what I'm trying to say.

<CreaturFile>
  <CreatureFile.Monsters>
    <Monster Name="Kobold" x:Name="Mepo"/>
    <Monster Name="Goblin"/>
  </CreatureFile.Monsters>
  <CreatureFile.Encounters>
    <Encounter>
      <Reference ElementName="Mepo"/>
    </Encounter>
  </CreatureFile.Encounters>
 </CreatureFile>