Added ref to ABNF and RFC5234 as per Roman Danyliw's Discuss 2025/7/20

Author: douglm

sources/sections-ietf/02-conventions.adoc

@@ -7,6 +7,8 @@ The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
 interpreted as described in BCP 14 <<RFC2119>> <<RFC8174>> when, and
 only when, they appear in all capitals, as shown here.
 
+The notation used in this memo to (re-)define iCalendar elements is the ABNF notation of <<RFC5234>> as used by <<RFC5545>>. Any syntax elements shown below that are not explicitly defined in this specification come from iCalendar <<RFC5545>>.
+
 Calendaring and scheduling roles are referred to in quoted-strings of
 text with the first character of each word in upper case.  For
 example, "Organizer" refers to a role of a "Calendar User" (CU)

sources/sections-ietf/98-references.adoc

@@ -5,6 +5,7 @@
 * [[[RFC2119,RFC 2119]]]
 * [[[RFC4791,RFC 4791]]]
 * [[[RFC4918,RFC 4918]]]
+* [[[RFC5234,RFC 5234]]]
 * [[[RFC5545,RFC 5545]]]
 * [[[RFC5546,RFC 5546]]]
 * [[[RFC8174,RFC 8174]]]