There is one potential procedural with it, as one normative reference:
[5] Berners-Lee, T., "Universal Resource Identifiers in WWW: A
Unifying Syntax for the Expression of Names and Addresses of
Objects on the Network as used in the World-Wide Web", RFC 1630,
June 1994.
.. is Informational. The rules have been stretched now and then (e.g.,
when referring to hash functions defined in informational RFCs but the
function is really defined by some external document), not sure if this
is one similar case. Maybe a different ref would be findable on URIs?