mysterious 'cn' response parameter

[Spongman]

TS-0004 (versions 2 through 4) all contain this paragraph (in H.2.2):

if the receiver CSE supports the <request> resource type it shall provide a reference to the created resource in the 'cn' parameter of the response.

• what is this cn parameter?
• how is this reference supposed to be serialized?
• can we get an example (in json & xml) ?