Message
Unregistered link relationship: foo
Explanation
The current values for the Registry of Atom Link Relations are as follows:
alternatecurrentenclosureeditedit-mediafirstlastlicensenextnext-archivepaymentprev-archivepreviousrelatedrepliesselfserviceupvia
Solution
Change the attribute value to one in the list.
If a value other than one of the above is desired, either register the relation with the IANA registry, or express the rel as a fully qualified URI.
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