https://app.knowbase.one/vault/rfc/docid/5142
RFC4715: The Integrated Services Digital Network (ISDN) Subaddress Encoding Type for tel URI
Network Working Group M. Munakata Request for Comments: 4715 S. Schubert Category: Informational T. Ohba NTT ...
https://app.knowbase.one/vault/rfc/docid/5705
RFC5233: Sieve Email Filtering: Subaddress Extension
Network Working Group K. Murchison Request for Comments: 5233 Carnegie Mellon University Obsoletes: 3598 January 2008 Category: Standards Track Sieve Email Filtering: Subaddress...