0, "tab" (U+0009), "LF" (U+000A),
        "FF" (U+000C), "CR" (U+000D) or "," (U+002C) characters can be used as a
        valid link relation. To promote interoperability, Activity Streams 2.0
        implementations MUST only use link relations that are syntactically
        valid in terms of both the [[RFC5988]] and [[HTML5]] definitions.
        Implementations MAY use link relation values that are not registered.
      </p>

      <p>
        Note that the <a>Link</a> and <a>Object</a> types are disjoi