DataContractSerializer: preserve references

Question

Just a question of curiosity. When i preserve object refernces while serializing an object graph with DataContractSerializer the xml emitted where there are refrences looks like this:

<test z:Ref="1" and i:nil="true" />

Can anybody tell me why it says i:nil="true" here? Why not just the reference?

Answer 1

This is because the content of the test element is empty. i:nil="true" is necessary so that the content will validate.