Hi,   I have reviewed draft-ietf-calext-extensions-03 as part of the Operational directorate's ongoing effort to review all IETF documents being processed by the IESG.  These comments were written with the intent of improving the operational aspects of the IETF drafts. Comments that are not addressed in last call may be included in AD reviews during the IESG review.  Document editors and WG chairs should treat these comments just like any other last call comments.   This I-D is an application protocol document which extends the iCalendar definition in RFC 5545, modifies some existing properties and defines new properties and elements that bring into the standard extension elements added by vendors into their specification.     An RFC 5706 review does not apply because deals with an application protocol, with no direct impact on the Internet or IP networks functionality or operations. Section 3 explains the mechanisms used to ensure backwards compatibility of the extension properties. These mechanisms have already been used by vendors and also in a couple of standard RFCs that updated RFC 5545.   I believe the document is 'Ready' for publication from the OPS-DIR perspective.   Regards,   Dan