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RFC 5546

iCalendar Transport-Independent Interoperability Protocol (iTIP)

Pages: 133
Proposed Standard
Errata
Obsoletes:  2446
Updates:  5545
Updated by:  6638
Part 2 of 5 – Pages 13 to 36
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Top   ToC   RFC5546 - Page 13   prevText

3. Application Protocol Elements

iTIP messages are "text/calendar" MIME entities that contain calendaring and scheduling information. The particular type of iCalendar message is referred to as the "method type". Each method type is identified by a "METHOD" property specified as part of the "text/calendar" content type. The table below shows various
Top   ToC   RFC5546 - Page 14
   combinations of calendar components and the method types that this
   specification supports.

        +----------------+--------+-------+----------+-----------+
        |                | VEVENT | VTODO | VJOURNAL | VFREEBUSY |
        +----------------+--------+-------+----------+-----------+
        | PUBLISH        | Yes    | Yes   | Yes      | Yes       |
        | REQUEST        | Yes    | Yes   | No       | Yes       |
        | REFRESH        | Yes    | Yes   | No       | No        |
        | CANCEL         | Yes    | Yes   | Yes      | No        |
        | ADD            | Yes    | Yes   | Yes      | No        |
        | REPLY          | Yes    | Yes   | No       | Yes       |
        | COUNTER        | Yes    | Yes   | No       | No        |
        | DECLINECOUNTER | Yes    | Yes   | No       | No        |
        +----------------+--------+-------+----------+-----------+

   Each method type is defined in terms of its associated components and
   properties.  Some components and properties are required, some are
   optional, and others are excluded.  The restrictions are expressed in
   this document using a simple "restriction table".  The first column
   indicates the name of a component or property.  Properties of the
   iCalendar object are not indented.  Properties of a component are
   indented.  The second column (the "Presence" column) indicates
   whether or not a component or property should be present and, if
   present, how many times it can occur.  The third column contains
   comments for further clarification.

   The presence column uses the following values to assert whether a
   property is required or optional, and the number of times it may
   appear in the iCalendar object.

   +----------------+--------------------------------------------------+
   | Presence Value | Description                                      |
   +----------------+--------------------------------------------------+
   | 1              | One instance MUST be present.                    |
   | 1+             | At least one instance MUST be present.           |
   | 0              | Instances of this property MUST NOT be present.  |
   | 0+             | Multiple instances MAY be present.               |
   | 0 or 1         | Up to 1 instance of this property MAY be         |
   |                | present.                                         |
   +----------------+--------------------------------------------------+

   The tables also call out "IANA-PROPERTY", "X-PROPERTY", "IANA-
   COMPONENT", and "X-COMPONENT" to show where registered and
   experimental property and component extensions can appear.  The
   tables do not lay out the restrictions of property parameters.  Those
   restrictions are defined in [RFC5545].
Top   ToC   RFC5546 - Page 15

3.1. Common Component Restriction Tables

3.1.1. VCALENDAR

The restriction table below applies to properties of the iCalendar object. That is, the properties at the outermost scope. +-----------------------------------------------------+ | Constraints for Properties in a VCALENDAR Component | +-----------------------------------------------------+ +--------------------+----------+--------------------+ | Component/Property | Presence | Comment | +--------------------+----------+--------------------+ | CALSCALE | 0 or 1 | | | PRODID | 1 | | | VERSION | 1 | Value MUST be 2.0. | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | +--------------------+----------+--------------------+

3.1.2. VTIMEZONE

"VTIMEZONE" components may be referred to by other components via a "TZID" parameter on a "DATETIME" value type. The property restrictions in the table below apply to any "VTIMEZONE" component in an iTIP message. +--------------------------------------+ | Constraints for VTIMEZONE Components | +--------------------------------------+
Top   ToC   RFC5546 - Page 16
   +--------------------+----------+-----------------------------------+
   | Component/Property | Presence | Comment                           |
   +--------------------+----------+-----------------------------------+
   | VTIMEZONE          | 0+       | MUST be present if any date/time  |
   |                    |          | refers to timezone.               |
   |   DAYLIGHT         | 0+       | MUST be one or more of either     |
   |                    |          | STANDARD or DAYLIGHT.             |
   |     COMMENT        | 0+       |                                   |
   |     DTSTART        | 1        | MUST be local time format.        |
   |     RDATE          | 0+       |                                   |
   |     RRULE          | 0 or 1   |                                   |
   |     TZNAME         | 0+       |                                   |
   |     TZOFFSETFROM   | 1        |                                   |
   |     TZOFFSETTO     | 1        |                                   |
   |     IANA-PROPERTY  | 0+       |                                   |
   |     X-PROPERTY     | 0+       |                                   |
   |   LAST-MODIFIED    | 0 or 1   |                                   |
   |   STANDARD         | 0+       | MUST be one or more of either     |
   |                    |          | STANDARD or DAYLIGHT.             |
   |     COMMENT        | 0+       |                                   |
   |     DTSTART        | 1        | MUST be local time format.        |
   |     RDATE          | 0+       | If present, RRULE MUST NOT be     |
   |                    |          | present.                          |
   |     RRULE          | 0 or 1   | If present, RDATE MUST NOT be     |
   |                    |          | present.                          |
   |     TZNAME         | 0+       |                                   |
   |     TZOFFSETFROM   | 1        |                                   |
   |     TZOFFSETTO     | 1        |                                   |
   |     IANA-PROPERTY  | 0+       |                                   |
   |     X-PROPERTY     | 0+       |                                   |
   |   TZID             | 1        |                                   |
   |   TZURL            | 0 or 1   |                                   |
   |   IANA-PROPERTY    | 0+       |                                   |
   |   X-PROPERTY       | 0+       |                                   |
   +--------------------+----------+-----------------------------------+
Top   ToC   RFC5546 - Page 17

3.1.3. VALARM

The property restrictions in the table below apply to any "VALARM" component in an iTIP message. +-----------------------------------+ | Constraints for VALARM Components | +-----------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | VALARM | 0+ | | | ACTION | 1 | | | ATTACH | 0+ | | | ATTENDEE | 0+ | | | DESCRIPTION | 0 or 1 | | | DURATION | 0 or 1 | If present, REPEAT MUST be | | | | present. | | REPEAT | 0 or 1 | If present, DURATION MUST be | | | | present. | | SUMMARY | 0 or 1 | | | TRIGGER | 1 | | | IANA-PROPERTY | 0+ | | | X-PROPERTY | 0+ | | +--------------------+----------+-----------------------------------+

3.2. Methods for VEVENT Calendar Components

This section defines the property set restrictions for the method types that are applicable to the "VEVENT" calendar component. Each method is defined using a table that clarifies the property constraints that define the particular method. The following summarizes the methods that are defined for the "VEVENT" calendar component.
Top   ToC   RFC5546 - Page 18
   +----------------+--------------------------------------------------+
   | Method         | Description                                      |
   +----------------+--------------------------------------------------+
   | PUBLISH        | Post notification of an event.  Used primarily   |
   |                | as a method of advertising the existence of an   |
   |                | event.                                           |
   |                |                                                  |
   | REQUEST        | Make a request for an event.  This is an         |
   |                | explicit invitation to one or more Attendees.    |
   |                | Event requests are also used to update or change |
   |                | an existing event.  Clients that cannot handle   |
   |                | REQUEST MAY degrade the event to view it as a    |
   |                | PUBLISH.                                         |
   |                |                                                  |
   | REPLY          | Reply to an event request.  Clients may set      |
   |                | their status (PARTSTAT) to ACCEPTED, DECLINED,   |
   |                | TENTATIVE, or DELEGATED.                         |
   |                |                                                  |
   | ADD            | Add one or more instances to an existing event.  |
   |                |                                                  |
   | CANCEL         | Cancel one or more instances of an existing      |
   |                | event.                                           |
   |                |                                                  |
   | REFRESH        | A request is sent to an Organizer by an Attendee |
   |                | asking for the latest version of an event to be  |
   |                | resent to the requester.                         |
   |                |                                                  |
   | COUNTER        | Counter a REQUEST with an alternative proposal.  |
   |                | Sent by an Attendee to the Organizer.            |
   |                |                                                  |
   | DECLINECOUNTER | Decline a counter proposal.  Sent to an Attendee |
   |                | by the Organizer.                                |
   +----------------+--------------------------------------------------+

3.2.1. PUBLISH

The "PUBLISH" method in a "VEVENT" calendar component is an unsolicited posting of an iCalendar object. Any CU may add published components to their calendar. The "Organizer" MUST be present in a published iCalendar component. "Attendees" MUST NOT be present. Its expected usage is for encapsulating an arbitrary event as an iCalendar object. The "Organizer" may subsequently update (with another "PUBLISH" method), add instances to (with an "ADD" method), or cancel (with a "CANCEL" method) a previously published "VEVENT" calendar component. This method type is an iCalendar object that conforms to the following property constraints:
Top   ToC   RFC5546 - Page 19
             +----------------------------------------------+
             | Constraints for a METHOD:PUBLISH of a VEVENT |
             +----------------------------------------------+

   +--------------------+----------+-----------------------------------+
   | Component/Property | Presence | Comment                           |
   +--------------------+----------+-----------------------------------+
   | METHOD             | 1        | MUST equal PUBLISH.               |
   |                    |          |                                   |
   | VEVENT             | 1+       |                                   |
   |   DTSTAMP          | 1        |                                   |
   |   DTSTART          | 1        |                                   |
   |   ORGANIZER        | 1        |                                   |
   |   SUMMARY          | 1        | Can be null.                      |
   |   UID              | 1        |                                   |
   |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
   |                    |          | of a recurring calendar           |
   |                    |          | component.  Otherwise, it MUST    |
   |                    |          | NOT be present.                   |
   |   SEQUENCE         | 0 or 1   | MUST be present if value is       |
   |                    |          | greater than 0; MAY be present if |
   |                    |          | 0.                                |
   |   ATTACH           | 0+       |                                   |
   |   CATEGORIES       | 0+       |                                   |
   |   CLASS            | 0 or 1   |                                   |
   |   COMMENT          | 0+       |                                   |
   |   CONTACT          | 0 or 1   |                                   |
   |   CREATED          | 0 or 1   |                                   |
   |   DESCRIPTION      | 0 or 1   | Can be null.                      |
   |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
   |                    |          | present.                          |
   |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
   |                    |          | present.                          |
   |   EXDATE           | 0+       |                                   |
   |   GEO              | 0 or 1   |                                   |
   |   LAST-MODIFIED    | 0 or 1   |                                   |
   |   LOCATION         | 0 or 1   |                                   |
   |   PRIORITY         | 0 or 1   |                                   |
   |   RDATE            | 0+       |                                   |
   |   RELATED-TO       | 0+       |                                   |
   |   RESOURCES        | 0+       |                                   |
   |   RRULE            | 0 or 1   |                                   |
   |   STATUS           | 0 or 1   | MAY be one of                     |
   |                    |          | TENTATIVE/CONFIRMED/CANCELLED.    |
   |   TRANSP           | 0 or 1   |                                   |
   |   URL              | 0 or 1   |                                   |
   |   IANA-PROPERTY    | 0+       |                                   |
   |   X-PROPERTY       | 0+       |                                   |
Top   ToC   RFC5546 - Page 20
   |   ATTENDEE         | 0        |                                   |
   |   REQUEST-STATUS   | 0        |                                   |
   |                    |          |                                   |
   |   VALARM           | 0+       |                                   |
   |                    |          |                                   |
   | VFREEBUSY          | 0        |                                   |
   |                    |          |                                   |
   | VJOURNAL           | 0        |                                   |
   |                    |          |                                   |
   | VTODO              | 0        |                                   |
   |                    |          |                                   |
   | VTIMEZONE          | 0+       | MUST be present if any date/time  |
   |                    |          | refers to a timezone.             |
   |                    |          |                                   |
   | IANA-COMPONENT     | 0+       |                                   |
   | X-COMPONENT        | 0+       |                                   |
   +--------------------+----------+-----------------------------------+

3.2.2. REQUEST

The "REQUEST" method in a "VEVENT" component provides the following scheduling functions: o Invite "Attendees" to an event. o Reschedule an existing event. o Response to a "REFRESH" request. o Update the details of an existing event, without rescheduling it. o Update the status of "Attendees" of an existing event, without rescheduling it. o Reconfirm an existing event, without rescheduling it. o Forward a "VEVENT" to another uninvited CU. o For an existing "VEVENT" calendar component, delegate the role of "Attendee" to another CU. o For an existing "VEVENT" calendar component, change the role of "Organizer" to another CU. The "Organizer" originates the "REQUEST". The recipients of the "REQUEST" method are the CUs invited to the event, the "Attendees". "Attendees" use the "REPLY" method to convey attendance status to the "Organizer".
Top   ToC   RFC5546 - Page 21
   The "UID" and "SEQUENCE" properties are used to distinguish the
   various uses of the "REQUEST" method.  If the "UID" property value in
   the "REQUEST" is not found on the recipient's calendar, then the
   "REQUEST" is for a new "VEVENT" calendar component.  If the "UID"
   property value is found on the recipient's calendar, then the
   "REQUEST" is for a rescheduling, an update, or a reconfirmation of
   the "VEVENT" calendar component.

   For the "REQUEST" method, multiple "VEVENT" components in a single
   iCalendar object are only permitted for components with the same
   "UID" property.  That is, a series of recurring events may have
   instance-specific information.  In this case, multiple "VEVENT"
   components are needed to express the entire series.

   This method type is an iCalendar object that conforms to the
   following property constraints:

             +----------------------------------------------+
             | Constraints for a METHOD:REQUEST of a VEVENT |
             +----------------------------------------------+

   +--------------------+----------+-----------------------------------+
   | Component/Property | Presence | Comment                           |
   +--------------------+----------+-----------------------------------+
   | METHOD             | 1        | MUST be REQUEST.                  |
   |                    |          |                                   |
   | VEVENT             | 1+       | All components MUST have the same |
   |                    |          | UID.                              |
   |   ATTENDEE         | 1+       |                                   |
   |   DTSTAMP          | 1        |                                   |
   |   DTSTART          | 1        |                                   |
   |   ORGANIZER        | 1        |                                   |
   |   SEQUENCE         | 0 or 1   | MUST be present if value is       |
   |                    |          | greater than 0; MAY be present if |
   |                    |          | 0.                                |
   |   SUMMARY          | 1        | Can be null.                      |
   |   UID              | 1        |                                   |
   |   ATTACH           | 0+       |                                   |
   |   CATEGORIES       | 0+       |                                   |
   |   CLASS            | 0 or 1   |                                   |
   |   COMMENT          | 0+       |                                   |
   |   CONTACT          | 0+       |                                   |
   |   CREATED          | 0 or 1   |                                   |
   |   DESCRIPTION      | 0 or 1   | Can be null.                      |
   |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
   |                    |          | present.                          |
Top   ToC   RFC5546 - Page 22
   |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
   |                    |          | present.                          |
   |   EXDATE           | 0+       |                                   |
   |   GEO              | 0 or 1   |                                   |
   |   LAST-MODIFIED    | 0 or 1   |                                   |
   |   LOCATION         | 0 or 1   |                                   |
   |   PRIORITY         | 0 or 1   |                                   |
   |   RDATE            | 0+       |                                   |
   |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
   |                    |          | of a recurring calendar           |
   |                    |          | component.  Otherwise, it MUST    |
   |                    |          | NOT be present.                   |
   |   RELATED-TO       | 0+       |                                   |
   |   REQUEST-STATUS   | 0        |                                   |
   |   RESOURCES        | 0+       |                                   |
   |   RRULE            | 0 or 1   |                                   |
   |   STATUS           | 0 or 1   | MAY be one of                     |
   |                    |          | TENTATIVE/CONFIRMED.              |
   |   TRANSP           | 0 or 1   |                                   |
   |   URL              | 0 or 1   |                                   |
   |   IANA-PROPERTY    | 0+       |                                   |
   |   X-PROPERTY       | 0+       |                                   |
   |                    |          |                                   |
   |   VALARM           | 0+       |                                   |
   |                    |          |                                   |
   | VTIMEZONE          | 0+       | MUST be present if any date/time  |
   |                    |          | refers to a timezone.             |
   |                    |          |                                   |
   | IANA-COMPONENT     | 0+       |                                   |
   | X-COMPONENT        | 0+       |                                   |
   |                    |          |                                   |
   | VFREEBUSY          | 0        |                                   |
   |                    |          |                                   |
   | VJOURNAL           | 0        |                                   |
   |                    |          |                                   |
   | VTODO              | 0        |                                   |
   +--------------------+----------+-----------------------------------+

3.2.2.1. Rescheduling an Event
The "REQUEST" method may be used to reschedule an event. A rescheduled event involves a change to the existing event in terms of its time or recurrence intervals and possibly the location or description. If the recipient CUA of a "REQUEST" method finds that the "UID" property value already exists on the calendar but that the "SEQUENCE" (or "DTSTAMP") property value in the "REQUEST" method is greater than the value for the existing event, then the "REQUEST" method describes a rescheduling of the event.
Top   ToC   RFC5546 - Page 23
3.2.2.2. Updating or Reconfirmation of an Event
The "REQUEST" method may be used to update or reconfirm an event. An update to an existing event does not involve changes to the time or recurrence intervals, and might not involve a change to the location or description for the event. If the recipient CUA of a "REQUEST" method finds that the "UID" property value already exists on the calendar and that the "SEQUENCE" property value in the "REQUEST" is the same as the value for the existing event, then the "REQUEST" method describes an update of the event details, but not a rescheduling of the event. The update "REQUEST" method is the appropriate response to a "REFRESH" method sent from an "Attendee" to the "Organizer" of an event. The "Organizer" of an event may also send unsolicited "REQUEST" methods. The unsolicited "REQUEST" methods may be used to update the details of the event without rescheduling it, to update the "PARTSTAT" parameter of "Attendees", or to reconfirm the event.
3.2.2.3. Delegating an Event to Another CU
Some calendar and scheduling systems allow "Attendees" to delegate their presence at an event to another "Calendar User". iTIP supports this concept using the following workflow. Any "Attendee" may delegate their right to participate in a calendar "VEVENT" to another CU. The implication is that the delegate participates in lieu of the original "Attendee", NOT in addition to the "Attendee". The delegator MUST notify the "Organizer" of this action using the steps outlined below. Implementations may support or restrict delegation as they see fit. For instance, some implementations may restrict a delegate from delegating a "REQUEST" to another CU. The "Delegator" of an event forwards the existing "REQUEST" to the "Delegate". The "REQUEST" method MUST include an "ATTENDEE" property with the calendar address of the "Delegate". The "Delegator" MUST also send a "REPLY" method to the "Organizer" with the "Delegator's" "ATTENDEE" property "PARTSTAT" parameter value set to "DELEGATED". In addition, the "DELEGATED-TO" parameter MUST be included with the calendar address of the "Delegate". Also, a new "ATTENDEE" property for the "Delegate" MUST be included and must specify the calendar user address set in the "DELEGATED-TO" parameter, as above. In response to the request, the "Delegate" MUST send a "REPLY" method to the "Organizer", and optionally to the "Delegator". The "REPLY" method SHOULD include the "ATTENDEE" property with the "DELEGATED- FROM" parameter value of the "Delegator's" calendar address.
Top   ToC   RFC5546 - Page 24
   The "Delegator" may continue to receive updates to the event even
   though they will not be attending.  This is accomplished by the
   "Delegator" setting their "role" attribute to "NON-PARTICIPANT" in
   the "REPLY" to the "Organizer".

3.2.2.4. Changing the Organizer
The situation may arise where the "Organizer" of a "VEVENT" is no longer able to perform the "Organizer" role and abdicates without passing on the "Organizer" role to someone else. When this occurs, the "Attendees" of the "VEVENT" may use out-of-band mechanisms to communicate the situation and agree upon a new "Organizer". The new "Organizer" should then send out a new "REQUEST" with a modified version of the "VEVENT" in which the "SEQUENCE" number has been incremented and the "ORGANIZER" property has been changed to the new "Organizer".
3.2.2.5. Sending on Behalf of the Organizer
There are a number of scenarios that support the need for a "Calendar User" to act on behalf of the "Organizer" without explicit role changing. This might be the case if the CU designated as "Organizer" is sick or unable to perform duties associated with that function. In these cases, iTIP supports the notion of one CU acting on behalf of another. Using the "SENT-BY" parameter, a "Calendar User" could send an updated "VEVENT" "REQUEST". In the case where one CU sends on behalf of another CU, the "Attendee" responses are still directed back towards the CU designated as "Organizer".
3.2.2.6. Forwarding to an Uninvited CU
An "Attendee" invited to a "VEVENT" calendar component may send the "VEVENT" calendar component to another new CU not previously associated with the "VEVENT" calendar component. The current "Attendee" invited to the "VEVENT" calendar component does this by forwarding the original "REQUEST" method to the new CU. The new CU can send a "REPLY" to the "Organizer" of the "VEVENT" calendar component. The reply contains an "ATTENDEE" property for the new CU. The "Organizer" ultimately decides whether or not the new CU becomes part of the event and is not obligated to do anything with a "REPLY" from a new (uninvited) CU. If the "Organizer" does not want the new CU to be part of the event, the new "ATTENDEE" property is not added to the "VEVENT" calendar component. The "Organizer" MAY send the CU a "CANCEL" message to indicate that they will not be added to the event. If the "Organizer" decides to add the new CU, the new "ATTENDEE" property is added to the "VEVENT" calendar component. Furthermore, the "Organizer" is free to change any "ATTENDEE"
Top   ToC   RFC5546 - Page 25
   property parameter from the values supplied by the new CU to
   something the "Organizer" considers appropriate.  The "Organizer"
   SHOULD send the new CU a "REQUEST" message to inform them that they
   have been added.

   When forwarding a "REQUEST" to another CU, the forwarding "Attendee"
   MUST NOT make changes to the original message.

3.2.2.7. Updating Attendee Status
The "Organizer" of an event may also request updated status from one or more "Attendees". The "Organizer" sends a "REQUEST" method to the "Attendee" and sets the "ATTENDEE;RSVP=TRUE" property parameter. The "SEQUENCE" property for the event is not changed from its previous value. A recipient will determine that the only change in the "REQUEST" is that their "RSVP" property parameter indicates a request for updated status. The recipient SHOULD respond with a "REPLY" method indicating their current status with respect to the "REQUEST".

3.2.3. REPLY

The "REPLY" method in a "VEVENT" calendar component is used to respond (e.g., accept or decline) to a "REQUEST" or to reply to a delegation "REQUEST". When used to provide a delegation response, the "Delegator" SHOULD include the calendar address of the "Delegate" on the "DELEGATED-TO" property parameter of the "Delegator's" "ATTENDEE" property. The "Delegate" SHOULD include the calendar address of the "Delegator" on the "DELEGATED-FROM" property parameter of the "Delegate's" "ATTENDEE" property. The "REPLY" method is also used when processing of a "REQUEST" fails. Depending on the value of the "REQUEST-STATUS" property, no scheduling action may have been performed. The "Organizer" of an event may receive the "REPLY" method from a CU not in the original "REQUEST". For example, a "REPLY" may be received from a "Delegate" to an event. In addition, the "REPLY" method may be received from an unknown CU (a "Party Crasher"). This uninvited "Attendee" may be accepted, or the "Organizer" may cancel the event for the uninvited "Attendee" by sending a "CANCEL" method to the uninvited "Attendee". An "Attendee" MAY include a message to the "Organizer" using the "COMMENT" property. For example, if the user indicates tentative acceptance and wants to let the "Organizer" know why, the reason can be expressed in the "COMMENT" property value.
Top   ToC   RFC5546 - Page 26
   The "Organizer" may also receive a "REPLY" from one CU on behalf of
   another.  Like the scenario enumerated above for the "Organizer",
   "Attendees" may have another CU respond on their behalf.  This is
   done using the "SENT-BY" parameter.

   The optional properties listed in the table below (those listed as
   "0+" or "0 or 1") MUST NOT be changed from those of the original
   request.  If property changes are desired, the "COUNTER" message must
   be used.

   This method type is an iCalendar object that conforms to the
   following property constraints:

              +--------------------------------------------+
              | Constraints for a METHOD:REPLY of a VEVENT |
              +--------------------------------------------+

   +--------------------+----------+-----------------------------------+
   | Component/Property | Presence | Comment                           |
   +--------------------+----------+-----------------------------------+
   | METHOD             | 1        | MUST be REPLY.                    |
   |                    |          |                                   |
   | VEVENT             | 1+       | All components MUST have the same |
   |                    |          | UID.                              |
   |   ATTENDEE         | 1        | MUST be the address of the        |
   |                    |          | Attendee replying.                |
   |   DTSTAMP          | 1        |                                   |
   |   ORGANIZER        | 1        |                                   |
   |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
   |                    |          | of a recurring calendar           |
   |                    |          | component.  Otherwise, it MUST    |
   |                    |          | NOT be present.                   |
   |   UID              | 1        | MUST be the UID of the original   |
   |                    |          | REQUEST.                          |
   |   SEQUENCE         | 0 or 1   | If non-zero, MUST be the sequence |
   |                    |          | number of the original REQUEST.   |
   |                    |          | MAY be present if 0.              |
   |   ATTACH           | 0+       |                                   |
   |   CATEGORIES       | 0+       |                                   |
   |   CLASS            | 0 or 1   |                                   |
   |   COMMENT          | 0+       |                                   |
   |   CONTACT          | 0+       |                                   |
   |   CREATED          | 0 or 1   |                                   |
   |   DESCRIPTION      | 0 or 1   |                                   |
   |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
   |                    |          | present.                          |
   |   DTSTART          | 0 or 1   |                                   |
Top   ToC   RFC5546 - Page 27
   |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
   |                    |          | present.                          |
   |   EXDATE           | 0+       |                                   |
   |   GEO              | 0 or 1   |                                   |
   |   LAST-MODIFIED    | 0 or 1   |                                   |
   |   LOCATION         | 0 or 1   |                                   |
   |   PRIORITY         | 0 or 1   |                                   |
   |   RDATE            | 0+       |                                   |
   |   RELATED-TO       | 0+       |                                   |
   |   RESOURCES        | 0+       |                                   |
   |   REQUEST-STATUS   | 0+       |                                   |
   |   RRULE            | 0 or 1   |                                   |
   |   STATUS           | 0 or 1   |                                   |
   |   SUMMARY          | 0 or 1   |                                   |
   |   TRANSP           | 0 or 1   |                                   |
   |   URL              | 0 or 1   |                                   |
   |   IANA-PROPERTY    | 0+       |                                   |
   |   X-PROPERTY       | 0+       |                                   |
   |                    |          |                                   |
   |   VALARM           | 0        |                                   |
   |                    |          |                                   |
   | VTIMEZONE          | 0 or 1   | MUST be present if any date/time  |
   |                    |          | refers to a timezone.             |
   |                    |          |                                   |
   | IANA-COMPONENT     | 0+       |                                   |
   | X-COMPONENT        | 0+       |                                   |
   |                    |          |                                   |
   | VFREEBUSY          | 0        |                                   |
   |                    |          |                                   |
   | VJOURNAL           | 0        |                                   |
   |                    |          |                                   |
   | VTODO              | 0        |                                   |
   +--------------------+----------+-----------------------------------+

3.2.4. ADD

The "ADD" method allows the "Organizer" to add one or more new instances to an existing "VEVENT" using a single iTIP message without having to send the entire "VEVENT" with all the existing instance data, as it would have to do if the "REQUEST" method were used. The "UID" must be that of the existing event. If the "UID" property value in the "ADD" is not found on the recipient's calendar, then the recipient SHOULD send a "REFRESH" to the "Organizer" in order to be updated with the latest version of the "VEVENT". If an "Attendee" implementation does not support the "ADD" method, it should respond with a "REQUEST-STATUS" value of 3.14 and ask for a "REFRESH".
Top   ToC   RFC5546 - Page 28
   When handling an "ADD" message, the "Attendee" treats each component
   in the "ADD" message as if it were referenced via an "RDATE" in the
   main component.

   This method type is an iCalendar object that conforms to the
   following property constraints:

               +------------------------------------------+
               | Constraints for a METHOD:ADD of a VEVENT |
               +------------------------------------------+

   +--------------------+----------+-----------------------------------+
   | Component/Property | Presence | Comment                           |
   +--------------------+----------+-----------------------------------+
   | METHOD             | 1        | MUST be ADD.                      |
   |                    |          |                                   |
   | VEVENT             | 1        |                                   |
   |   DTSTAMP          | 1        |                                   |
   |   DTSTART          | 1        |                                   |
   |   ORGANIZER        | 1        |                                   |
   |   SEQUENCE         | 1        | MUST be greater than 0.           |
   |   SUMMARY          | 1        | Can be null.                      |
   |   UID              | 1        | MUST match that of the original   |
   |                    |          | event.                            |
   |   ATTACH           | 0+       |                                   |
   |   ATTENDEE         | 0+       |                                   |
   |   CATEGORIES       | 0+       |                                   |
   |   CLASS            | 0 or 1   |                                   |
   |   COMMENT          | 0+       |                                   |
   |   CONTACT          | 0+       |                                   |
   |   CREATED          | 0 or 1   |                                   |
   |   DESCRIPTION      | 0 or 1   | Can be null.                      |
   |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
   |                    |          | present.                          |
   |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
   |                    |          | present.                          |
   |   GEO              | 0 or 1   |                                   |
   |   LAST-MODIFIED    | 0 or 1   |                                   |
   |   LOCATION         | 0 or 1   |                                   |
   |   PRIORITY         | 0 or 1   |                                   |
   |   RELATED-TO       | 0+       |                                   |
   |   RESOURCES        | 0+       |                                   |
   |   STATUS           | 0 or 1   | MAY be one of                     |
   |                    |          | TENTATIVE/CONFIRMED.              |
   |   TRANSP           | 0 or 1   |                                   |
   |   URL              | 0 or 1   |                                   |
   |   IANA-PROPERTY    | 0+       |                                   |
   |   X-PROPERTY       | 0+       |                                   |
Top   ToC   RFC5546 - Page 29
   |   EXDATE           | 0        |                                   |
   |   RECURRENCE-ID    | 0        |                                   |
   |   REQUEST-STATUS   | 0        |                                   |
   |   RDATE            | 0        |                                   |
   |   RRULE            | 0        |                                   |
   |                    |          |                                   |
   |   VALARM           | 0+       |                                   |
   |                    |          |                                   |
   | VTIMEZONE          | 0+       | MUST be present if any date/time  |
   |                    |          | refers to a timezone.             |
   |                    |          |                                   |
   | IANA-COMPONENT     | 0+       |                                   |
   | X-COMPONENT        | 0+       |                                   |
   |                    |          |                                   |
   | VFREEBUSY          | 0        |                                   |
   |                    |          |                                   |
   | VTODO              | 0        |                                   |
   |                    |          |                                   |
   | VJOURNAL           | 0        |                                   |
   +--------------------+----------+-----------------------------------+

3.2.5. CANCEL

The "CANCEL" method in a "VEVENT" calendar component is used to send a cancellation notice of an existing event request to the affected "Attendees". The message is sent by the "Organizer" of the event. For a recurring event, either the whole event or instances of an event may be cancelled. To cancel the complete range of a recurring event, the "UID" property value for the event MUST be specified and a "RECURRENCE-ID" MUST NOT be specified in the "CANCEL" method. In order to cancel an individual instance of the event, the "RECURRENCE-ID" property value for the event MUST be specified in the "CANCEL" method. There are two options for canceling a sequence of instances of a recurring "VEVENT" calendar component: a. The "RECURRENCE-ID" property for an instance in the sequence MUST be specified with the "RANGE" property parameter value of "THISANDFUTURE" to indicate cancellation of the specified "VEVENT" calendar component and all instances after. b. Individual recurrence instances may be cancelled by specifying multiple "VEVENT" components each with a "RECURRENCE-ID" property corresponding to one of the instances to be cancelled.
Top   ToC   RFC5546 - Page 30
   The "Organizer" MUST send a "CANCEL" message to each "Attendee"
   affected by the cancellation.  This can be done using a single
   "CANCEL" message for all "Attendees" or by using multiple messages
   with different subsets of the affected "Attendees" in each.

   When a "VEVENT" is cancelled, the "SEQUENCE" property value MUST be
   incremented as described in Section 2.1.4.

   This method type is an iCalendar object that conforms to the
   following property constraints:

              +---------------------------------------------+
              | Constraints for a METHOD:CANCEL of a VEVENT |
              +---------------------------------------------+

   +--------------------+----------+-----------------------------------+
   | Component/Property | Presence | Comment                           |
   +--------------------+----------+-----------------------------------+
   | METHOD             | 1        | MUST be CANCEL.                   |
   |                    |          |                                   |
   | VEVENT             | 1+       | All must have the same UID.       |
   |   ATTENDEE         | 0+       | MUST include some or all          |
   |                    |          | Attendees being removed from the  |
   |                    |          | event.  MUST include some or all  |
   |                    |          | Attendees if the entire event is  |
   |                    |          | cancelled.                        |
   |   DTSTAMP          | 1        |                                   |
   |   ORGANIZER        | 1        |                                   |
   |   SEQUENCE         | 1        |                                   |
   |   UID              | 1        | MUST be the UID of the original   |
   |                    |          | REQUEST.                          |
   |   COMMENT          | 0+       |                                   |
   |   ATTACH           | 0+       |                                   |
   |   CATEGORIES       | 0+       |                                   |
   |   CLASS            | 0 or 1   |                                   |
   |   CONTACT          | 0+       |                                   |
   |   CREATED          | 0 or 1   |                                   |
   |   DESCRIPTION      | 0 or 1   |                                   |
   |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
   |                    |          | present.                          |
   |   DTSTART          | 0 or 1   |                                   |
   |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
   |                    |          | present.                          |
   |   EXDATE           | 0+       |                                   |
   |   GEO              | 0 or 1   |                                   |
   |   LAST-MODIFIED    | 0 or 1   |                                   |
   |   LOCATION         | 0 or 1   |                                   |
   |   PRIORITY         | 0 or 1   |                                   |
Top   ToC   RFC5546 - Page 31
   |   RDATE            | 0+       |                                   |
   |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
   |                    |          | of a recurring calendar           |
   |                    |          | component.  Otherwise, it MUST    |
   |                    |          | NOT be present.                   |
   |   RELATED-TO       | 0+       |                                   |
   |   RESOURCES        | 0+       |                                   |
   |   RRULE            | 0 or 1   |                                   |
   |   STATUS           | 0 or 1   | MUST be set to CANCELLED to       |
   |                    |          | cancel the entire event.  If      |
   |                    |          | uninviting specific Attendees,    |
   |                    |          | then MUST NOT be included.        |
   |   SUMMARY          | 0 or 1   |                                   |
   |   TRANSP           | 0 or 1   |                                   |
   |   URL              | 0 or 1   |                                   |
   |   IANA-PROPERTY    | 0+       |                                   |
   |   X-PROPERTY       | 0+       |                                   |
   |   REQUEST-STATUS   | 0        |                                   |
   |                    |          |                                   |
   |   VALARM           | 0        |                                   |
   |                    |          |                                   |
   | VTIMEZONE          | 0+       | MUST be present if any date/time  |
   |                    |          | refers to a timezone.             |
   |                    |          |                                   |
   | IANA-COMPONENT     | 0+       |                                   |
   | X-COMPONENT        | 0+       |                                   |
   |                    |          |                                   |
   | VTODO              | 0        |                                   |
   |                    |          |                                   |
   | VJOURNAL           | 0        |                                   |
   |                    |          |                                   |
   | VFREEBUSY          | 0        |                                   |
   +--------------------+----------+-----------------------------------+

3.2.6. REFRESH

The "REFRESH" method in a "VEVENT" calendar component is used by "Attendees" of an existing event to request an updated description from the event "Organizer". The "REFRESH" method must specify the "UID" property of the event to update. A recurrence instance of an event may be requested by specifying the "RECURRENCE-ID" property corresponding to the associated event. The "Organizer" responds with the latest description and version of the event. This method type is an iCalendar object that conforms to the following property constraints:
Top   ToC   RFC5546 - Page 32
             +----------------------------------------------+
             | Constraints for a METHOD:REFRESH of a VEVENT |
             +----------------------------------------------+

   +--------------------+----------+-----------------------------------+
   | Component/Property | Presence | Comment                           |
   +--------------------+----------+-----------------------------------+
   | METHOD             | 1        | MUST be REFRESH.                  |
   |                    |          |                                   |
   | VEVENT             | 1        |                                   |
   |   ATTENDEE         | 1        | MUST be the address of requester. |
   |   DTSTAMP          | 1        |                                   |
   |   ORGANIZER        | 1        |                                   |
   |   UID              | 1        | MUST be the UID associated with   |
   |                    |          | original REQUEST.                 |
   |   COMMENT          | 0+       |                                   |
   |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
   |                    |          | of a recurring calendar           |
   |                    |          | component.  Otherwise, it MUST    |
   |                    |          | NOT be present.                   |
   |   IANA-PROPERTY    | 0+       |                                   |
   |   X-PROPERTY       | 0+       |                                   |
   |   ATTACH           | 0        |                                   |
   |   CATEGORIES       | 0        |                                   |
   |   CLASS            | 0        |                                   |
   |   CONTACT          | 0        |                                   |
   |   CREATED          | 0        |                                   |
   |   DESCRIPTION      | 0        |                                   |
   |   DTEND            | 0        |                                   |
   |   DTSTART          | 0        |                                   |
   |   DURATION         | 0        |                                   |
   |   EXDATE           | 0        |                                   |
   |   GEO              | 0        |                                   |
   |   LAST-MODIFIED    | 0        |                                   |
   |   LOCATION         | 0        |                                   |
   |   PRIORITY         | 0        |                                   |
   |   RDATE            | 0        |                                   |
   |   RELATED-TO       | 0        |                                   |
   |   REQUEST-STATUS   | 0        |                                   |
   |   RESOURCES        | 0        |                                   |
   |   RRULE            | 0        |                                   |
   |   SEQUENCE         | 0        |                                   |
   |   STATUS           | 0        |                                   |
   |   SUMMARY          | 0        |                                   |
   |   TRANSP           | 0        |                                   |
   |   URL              | 0        |                                   |
   |                    |          |                                   |
Top   ToC   RFC5546 - Page 33
   |   VALARM           | 0        |                                   |
   |                    |          |                                   |
   | VTIMEZONE          | 0+       |                                   |
   |                    |          |                                   |
   | IANA-COMPONENT     | 0+       |                                   |
   | X-COMPONENT        | 0+       |                                   |
   |                    |          |                                   |
   | VTODO              | 0        |                                   |
   |                    |          |                                   |
   | VJOURNAL           | 0        |                                   |
   |                    |          |                                   |
   | VFREEBUSY          | 0        |                                   |
   +--------------------+----------+-----------------------------------+

3.2.7. COUNTER

The "COUNTER" method for a "VEVENT" calendar component is used by an "Attendee" of an existing event to submit to the "Organizer" a counter proposal to the event. The "Attendee" sends this message to the "Organizer" of the event. The counter proposal is an iCalendar object consisting of a "VEVENT" calendar component that provides the complete description of the alternate event. The "Organizer" rejects the counter proposal by sending the "Attendee" a "DECLINECOUNTER" method. The "Organizer" accepts the counter proposal by rescheduling the event as described in Section 3.2.2.1, "Rescheduling an Event". The "Organizer's" CUA SHOULD send a "REQUEST" message to all "Attendees" affected by any change triggered by an accepted "COUNTER". This method type is an iCalendar object that conforms to the following property constraints: +----------------------------------------------+ | Constraints for a METHOD:COUNTER of a VEVENT | +----------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be COUNTER. | | | | | | VEVENT | 1 | | | DTSTAMP | 1 | | | DTSTART | 1 | |
Top   ToC   RFC5546 - Page 34
   |   ORGANIZER        | 1        | MUST be the Organizer of the      |
   |                    |          | original event.                   |
   |   SEQUENCE         | 1        | MUST echo the original SEQUENCE   |
   |                    |          | number.  MUST be present if       |
   |                    |          | non-zero.  MAY be present if      |
   |                    |          | zero.                             |
   |   SUMMARY          | 1        | Can be null.                      |
   |   UID              | 1        | MUST be the UID associated with   |
   |                    |          | the REQUEST being countered.      |
   |   ATTACH           | 0+       |                                   |
   |   ATTENDEE         | 0+       | Can also be used to propose other |
   |                    |          | Attendees.                        |
   |   CATEGORIES       | 0+       |                                   |
   |   CLASS            | 0 or 1   |                                   |
   |   COMMENT          | 0+       |                                   |
   |   CONTACT          | 0+       |                                   |
   |   CREATED          | 0 or 1   |                                   |
   |   DESCRIPTION      | 0 or 1   |                                   |
   |   DTEND            | 0 or 1   | If present, DURATION MUST NOT be  |
   |                    |          | present.                          |
   |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
   |                    |          | present.                          |
   |   EXDATE           | 0+       |                                   |
   |   GEO              | 0 or 1   |                                   |
   |   LAST-MODIFIED    | 0 or 1   |                                   |
   |   LOCATION         | 0 or 1   |                                   |
   |   PRIORITY         | 0 or 1   |                                   |
   |   RDATE            | 0+       |                                   |
   |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
   |                    |          | of a recurring calendar           |
   |                    |          | component.  Otherwise, it MUST    |
   |                    |          | NOT be present.                   |
   |   RELATED-TO       | 0+       |                                   |
   |   REQUEST-STATUS   | 0+       |                                   |
   |   RESOURCES        | 0+       |                                   |
   |   RRULE            | 0 or 1   |                                   |
   |   STATUS           | 0 or 1   | Value must be one of              |
   |                    |          | CONFIRMED/TENATIVE/CANCELLED.     |
   |   TRANSP           | 0 or 1   |                                   |
   |   URL              | 0 or 1   |                                   |
   |   IANA-PROPERTY    | 0+       |                                   |
   |   X-PROPERTY       | 0+       |                                   |
   |                    |          |                                   |
   |   VALARM           | 0+       |                                   |
   |                    |          |                                   |
   | VTIMEZONE          | 0+       | MUST be present if any date/time  |
   |                    |          | refers to a timezone.             |
   |                    |          |                                   |
Top   ToC   RFC5546 - Page 35
   | IANA-COMPONENT     | 0+       |                                   |
   | X-COMPONENT        | 0+       |                                   |
   |                    |          |                                   |
   | VTODO              | 0        |                                   |
   |                    |          |                                   |
   | VJOURNAL           | 0        |                                   |
   |                    |          |                                   |
   | VFREEBUSY          | 0        |                                   |
   +--------------------+----------+-----------------------------------+

3.2.8. DECLINECOUNTER

The "DECLINECOUNTER" method in a "VEVENT" calendar component is used by the "Organizer" of an event to reject a counter proposal submitted by an "Attendee". The "Organizer" must send the "DECLINECOUNTER" message to the "Attendee" that sent the "COUNTER" method to the "Organizer". This method type is an iCalendar object that conforms to the following property constraints: +-----------------------------------------------------+ | Constraints for a METHOD:DECLINECOUNTER of a VEVENT | +-----------------------------------------------------+ +--------------------+----------+-----------------------------------+ | Component/Property | Presence | Comment | +--------------------+----------+-----------------------------------+ | METHOD | 1 | MUST be DECLINECOUNTER. | | | | | | VEVENT | 1+ | All components MUST have the same | | | | UID. | | ATTENDEE | 1+ | MUST for all Attendees. | | DTSTAMP | 1 | | | ORGANIZER | 1 | | | SEQUENCE | 1 | MUST echo the original SEQUENCE | | | | number. | | UID | 1 | MUST echo original UID. | | ATTACH | 0+ | | | CATEGORIES | 0+ | | | CLASS | 0 or 1 | | | COMMENT | 0+ | | | CONTACT | 0+ | | | CREATED | 0 or 1 | | | DESCRIPTION | 0 or 1 | Can be null. | | DTSTART | 0 or 1 | | | DTEND | 0 or 1 | If present, DURATION MUST NOT be | | | | present. |
Top   ToC   RFC5546 - Page 36
   |   DURATION         | 0 or 1   | If present, DTEND MUST NOT be     |
   |                    |          | present.                          |
   |   EXDATE           | 0+       |                                   |
   |   GEO              | 0 or 1   |                                   |
   |   LAST-MODIFIED    | 0 or 1   |                                   |
   |   LOCATION         | 0 or 1   |                                   |
   |   PRIORITY         | 0 or 1   |                                   |
   |   RDATE            | 0+       |                                   |
   |   RECURRENCE-ID    | 0 or 1   | Only if referring to an instance  |
   |                    |          | of a recurring calendar           |
   |                    |          | component.  Otherwise, it MUST    |
   |                    |          | NOT be present.                   |
   |   RELATED-TO       | 0+       |                                   |
   |   REQUEST-STATUS   | 0+       |                                   |
   |   RESOURCES        | 0+       |                                   |
   |   RRULE            | 0 or 1   |                                   |
   |   STATUS           | 0 or 1   | MAY be one of                     |
   |                    |          | TENTATIVE/CONFIRMED.              |
   |   SUMMARY          | 0 or 1   | Can be null.                      |
   |   TRANSP           | 0 or 1   |                                   |
   |   URL              | 0 or 1   |                                   |
   |   IANA-PROPERTY    | 0+       |                                   |
   |   X-PROPERTY       | 0+       |                                   |
   |                    |          |                                   |
   |                    |          |                                   |
   | VTIMEZONE          | 0+       | MUST be present if any date/time  |
   |                    |          | refers to a timezone.             |
   |                    |          |                                   |
   | IANA-COMPONENT     | 0+       |                                   |
   | X-COMPONENT        | 0+       |                                   |
   |                    |          |                                   |
   |   VALARM           | 0        |                                   |
   | VFREEBUSY          | 0        |                                   |
   |                    |          |                                   |
   | VJOURNAL           | 0        |                                   |
   |                    |          |                                   |
   | VTODO              | 0        |                                   |
   +--------------------+----------+-----------------------------------+


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