incorporate RFC 9557 time zone extension into 'date-time' format

Author: gregsdennis

specs/jsonschema-validation.md

@@ -397,22 +397,24 @@ custom format values.
 These attributes apply to string instances.
 
 Date and time format names are derived from
+[RFC 9557, section 4.1](https://www.rfc-editor.org/info/rfc9557) which extends
 [RFC 3339, section 5.6](https://www.rfc-editor.org/info/rfc3339). The duration
 format is from the ISO 8601 ABNF as given in Appendix A of RFC 3339.
 
 - *date-time*: A string instance is valid against this attribute if it is a
-  valid representation according to the "date-time" ABNF rule (referenced above)
+  valid representation according to the "date-time" ABNF rule in RFC 3339,
+  optionally with the "time-zone" rule in RFC 9557
 - *date*: A string instance is valid against this attribute if it is a valid
-  representation according to the "full-date" ABNF rule (referenced above)
+  representation according to the "full-date" ABNF rule in RFC 3339
 - *time*: A string instance is valid against this attribute if it is a valid
-  representation according to the "full-time" ABNF rule (referenced above)
+  representation according to the "full-time" ABNF rule in RFC 3339
 - *duration*: A string instance is valid against this attribute if it is a valid
-  representation according to the "duration" ABNF rule (referenced above)
+  representation according to the "duration" ABNF rule in ISO 8601
 
 Implementations MAY support additional attributes using the other format names
 defined anywhere in that RFC. Implementations SHOULD NOT define extension
-attributes with any name matching an RFC 3339 format unless it validates
-according to the rules of that format.[^5]
+attributes with any name matching an RFC 3339, RFC 9557, or ISO 8601 format
+unless it validates according to the rules of that format.[^5]
 
 [^5]: There is not currently consensus on the need for supporting all RFC 3339
 formats, so this approach of reserving the namespace will encourage