In the Atom Format Specification replace section 3.4.1 "rel" Attribute with the following:
The "rel" attribute indicates the type of relationship that the link represents. Link constructs MUST have a rel attribute, whose value MUST be a string and MUST be one of the values enumerated in the Atom API specification or "other". If the attribute value is "other", the Link construct MUST have a reluri attribute.
Add section 3.4.5 "reluri" Attribute as follows:
See also PaceLinkRelMechanism