When more than one model is nested, the outer models will never contain data from the inner models (that is, the same fragment will never co-exist inside two models):
<order id="332">
<header>
<customer number="123">Joe</customer>
</header>
<order-items>
<order-item id='1'>
<product>1</product>
<quantity>2</quantity>
<price>8.80</price>
</order-item>
<order-item id='2'>
<product>2</product>
<quantity>2</quantity>
<price>8.80</price>
</order-item>
<order-item id='3'>
<product>3</product>
<quantity>2</quantity>
<price>8.80</price>
</order-item>
</order-items>
</order>