Specify navigation property binding combined with containment

This combination is not explicitly covered in the specification.

There are two sides to this problem:

• target entity sets for contained entities
• contained entity sets as target entity sets

The first problem can be solved by allowing <NavigationPropertyBinding> elements as children of <NavigationProperty> elements that specify ContainsTarget="true":
<NavigationProperty Name="Items" Type="Collection(Model.OrderItem)" ContainsTarget="true">
<NavigationPropertyBinding Path="Product" Target="Model.Container/Products"/>
</NavigationProperty>

The second problem is trickier: assume an Order contains Items and Shipments, and an Item refers to a single Shipment of the same Order and vice versa. Using paths that start at the type defining the containment navigation property, the Target would be "Shipments" and "Items".
<EntityType Name="Order">
<NavigationProperty Name="Items" Type="Collection(Model.OrderItem)" ContainsTarget="true">
<NavigationPropertyBinding Path="Shipment" Target="Shipments"/>
</NavigationProperty>
<NavigationProperty Name="Shipments" Type="Collection(Model.Shipment)" ContainsTarget="true">
<NavigationPropertyBinding Path="ShippedItems" Target="Items"/>
</NavigationProperty>
</EntityType>

<EntityType Name="OrderItem">
<NavigationProperty Name="Shipment" Type="Model.Shipment" Partner="ShippedItems"/>
</EntityType>

Slightly more complicated: Region contains SalesPeople and Customers, Customer has SalesRep that is a sales person from the same region. A Target can only be specified if Customer has an upward navigation to the containing Region: Target="Region/SalesPeople".

So target paths are either relative and start with a sibling of the parent (navigation property within the same type, entity set within the same container) or absolute and start with a qualified schema name.