@benpate According to RFC 8288 section 3.3, "registered" relation types can not contain a colon:
relation-type = reg-rel-type / ext-rel-type reg-rel-type = LOALPHA *( LOALPHA / DIGIT / "." / "-" ) ext-rel-type = URI"Unregistered" relation types should be URIs (though you can argue that intent:Follow is a URN).