http://www.rfc-editor.org/rfc/rfc8217.txt
RFC 8217: Clarifications for When to Use the name-addr Production in SIP Messages, R. Sparks2017-08-01T23:00:00-00:00This document updates RFC 3261 to state the constraint generically and clarifies that the constraint applies to all SIP header fields where there is a choice between using name-addr or addr-spec. It also updates the RFCs that define extension SIP header fields using the alternative to clarify that the constraint applies (RFCs 3325, 3515, 3892, 4508, 5002, 5318, 5360, and 5502).