    Internet Engineering Task Force (IETF)                          C. Daboo
    Request for Comments: 6638                                    Apple Inc.
    Updates: 4791, 5546                                      B. Desruisseaux
    Category: Standards Track                                         Oracle
    ISSN: 2070-1721                                                June 2012

                        Scheduling Extensions to CalDAV

    Abstract

       This document defines extensions to the Calendaring Extensions to
       WebDAV (CalDAV) "calendar-access" feature to specify a standard way
       of performing scheduling operations with iCalendar-based calendar
       components.  This document defines the "calendar-auto-schedule"
       feature of CalDAV.

    Status of This Memo

       This is an Internet Standards Track document.

       This document is a product of the Internet Engineering Task Force
       (IETF).  It represents the consensus of the IETF community.  It has
       received public review and has been approved for publication by the
       Internet Engineering Steering Group (IESG).  Further information on
       Internet Standards is available in Section 2 of RFC 5741.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       http://www.rfc-editor.org/info/rfc6638.

    Copyright Notice

       Copyright (c) 2012 IETF Trust and the persons identified as the
       document authors.  All rights reserved.

       This document is subject to BCP 78 and the IETF Trust's Legal
       Provisions Relating to IETF Documents
       (http://trustee.ietf.org/license-info) in effect on the date of
       publication of this document.  Please review these documents
       carefully, as they describe your rights and restrictions with respect
       to this document.  Code Components extracted from this document must
       include Simplified BSD License text as described in Section 4.e of
       the Trust Legal Provisions and are provided without warranty as
       described in the Simplified BSD License.

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    RFC 6638                    CalDAV Scheduling                  June 2012

       This document may contain material from IETF Documents or IETF
       Contributions published or made publicly available before November
       10, 2008.  The person(s) controlling the copyright in some of this
       material may not have granted the IETF Trust the right to allow
       modifications of such material outside the IETF Standards Process.
       Without obtaining an adequate license from the person(s) controlling
       the copyright in such materials, this document may not be modified
       outside the IETF Standards Process, and derivative works of it may
       not be created outside the IETF Standards Process, except to format
       it for publication as an RFC or to translate it into languages other
       than English.

    Table of Contents

       1. Introduction ....................................................5
          1.1. Terminology ................................................6
          1.2. Notational Conventions .....................................7
          1.3. XML Namespaces and Processing ..............................7
       2. Scheduling Support ..............................................8
          2.1. Scheduling Outbox Collection ...............................9
               2.1.1. CALDAV:schedule-outbox-URL Property ................10
          2.2. Scheduling Inbox Collection ...............................10
               2.2.1. CALDAV:schedule-inbox-URL Property .................11
          2.3. Calendaring Reports Extensions ............................12
          2.4. Additional Principal Properties ...........................12
               2.4.1. CALDAV:calendar-user-address-set Property ..........12
               2.4.2. CALDAV:calendar-user-type Property .................13
       3. Scheduling Operations ..........................................14
          3.1. Identifying Scheduling Object Resources ...................14
          3.2. Handling Scheduling Object Resources ......................15
               3.2.1. Organizer Scheduling Object Resources ..............15
                      3.2.1.1. Create ....................................16
                      3.2.1.2. Modify ....................................17
                      3.2.1.3. Remove ....................................18
               3.2.2. Attendee Scheduling Object Resources ...............18
                      3.2.2.1. Allowed "Attendee" Changes ................18
                      3.2.2.2. Create ....................................19
                      3.2.2.3. Modify ....................................20
                      3.2.2.4. Remove ....................................21
               3.2.3. HTTP Methods .......................................21
                      3.2.3.1. PUT .......................................22
                      3.2.3.2. DELETE ....................................22
                      3.2.3.3. COPY ......................................23
                      3.2.3.4. MOVE ......................................24

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               3.2.4. Additional Method Preconditions ....................24
                      3.2.4.1. CALDAV:unique-scheduling-object-resource
                               Precondition ..............................24
                      3.2.4.2. CALDAV:same-organizer-in-all-components
                               Precondition ..............................25
                      3.2.4.3. CALDAV:allowed-organizer-scheduling-
                                  object-change Precondition .............25
                      3.2.4.4. CALDAV:allowed-attendee-scheduling-
                                  object-change Precondition .............26
               3.2.5. DTSTAMP and SEQUENCE Properties ....................26
               3.2.6. Restrict Recurrence Instances Sent to "Attendees" ..27
               3.2.7. Forcing the Server to Send a Scheduling Message ....27
               3.2.8. "Attendee" Participation Status ....................28
               3.2.9. Schedule Status Values .............................29
               3.2.10. Avoiding Conflicts when Updating Scheduling Object
                       Resources .........................................31
                       3.2.10.1. PUT .....................................33
                       3.2.10.2. DELETE, COPY, or MOVE ...................33
       4. Processing Incoming Scheduling Messages ........................34
          4.1. Processing "Organizer" Requests, Additions, and
               Cancellations .............................................34
          4.2. Processing "Attendee" Replies .............................35
          4.3. Default Calendar Collection ...............................35
               4.3.1. Additional Method Preconditions ....................36
                      4.3.1.1. CALDAV:default-calendar-needed
                               Precondition ..............................36
                      4.3.1.2. CALDAV:valid-schedule-default-calendar-URL
                               Precondition ..............................36
       5. Request for Busy Time Information ..............................37
          5.1. Status Codes ..............................................38
          5.2. Additional Method Preconditions ...........................38
               5.2.1. CALDAV:valid-scheduling-message Precondition .......38
               5.2.2. CALDAV:valid-organizer Precondition ................39
       6. Scheduling Privileges ..........................................39
          6.1. Privileges on Scheduling Inbox Collections ................39
               6.1.1. CALDAV:schedule-deliver Privilege ..................40
               6.1.2. CALDAV:schedule-deliver-invite Privilege ...........40
               6.1.3. CALDAV:schedule-deliver-reply Privilege ............40
               6.1.4. CALDAV:schedule-query-freebusy Privilege ...........40
          6.2. Privileges on Scheduling Outbox Collections ...............40
               6.2.1. CALDAV:schedule-send Privilege .....................41
               6.2.2. CALDAV:schedule-send-invite Privilege ..............41
               6.2.3. CALDAV:schedule-send-reply Privilege ...............41
               6.2.4. CALDAV:schedule-send-freebusy Privilege ............41
          6.3. Aggregation of Scheduling Privileges ......................42

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       7. Additional iCalendar Property Parameters .......................42
          7.1. Schedule Agent Parameter ..................................42
          7.2. Schedule Force Send Parameter .............................44
          7.3. Schedule Status Parameter .................................45
       8. Additional Message Header Fields ...............................46
          8.1. Schedule-Reply Request Header .............................46
          8.2. Schedule-Tag Response Header ..............................46
          8.3. If-Schedule-Tag-Match Request Header ......................47
       9. Additional WebDAV Properties ...................................47
          9.1. CALDAV:schedule-calendar-transp Property ..................47
          9.2. CALDAV:schedule-default-calendar-URL Property .............48
          9.3. CALDAV:schedule-tag Property ..............................49
       10. XML Element Definitions .......................................50
          10.1. CALDAV:schedule-response XML Element .....................50
          10.2. CALDAV:response XML Element ..............................50
          10.3. CALDAV:recipient XML Element .............................50
          10.4. CALDAV:request-status XML Element ........................51
       11. Security Considerations .......................................51
          11.1. Preventing Denial-of-Service Attacks .....................51
          11.2. Verifying Scheduling Operations ..........................52
          11.3. Verifying Busy Time Information Requests .................52
          11.4. Privacy Issues ...........................................53
          11.5. Mitigation of iTIP Threats ...............................53
       12. IANA Considerations ...........................................54
          12.1. Message Header Field Registrations .......................54
               12.1.1. Schedule-Reply ....................................54
               12.1.2. Schedule-Tag ......................................54
               12.1.3. If-Schedule-Tag-Match .............................54
          12.2. iCalendar Property Parameter Registrations ...............55
          12.3. iCalendar REQUEST-STATUS Value Registrations .............55
          12.4. Additional iCalendar Elements Registries .................55
               12.4.1. Schedule Agent Values Registry ....................56
               12.4.2. Schedule Force Send Values Registry ...............56
       13. Acknowledgements ..............................................56
       14. References ....................................................57
          14.1. Normative References .....................................57
          14.2. Informative References ...................................58

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       Appendix A. Scheduling Privileges Summary .........................59
         A.1. Scheduling Inbox Privileges ................................59
         A.2. Scheduling Outbox Privileges ...............................60
       Appendix B. Example Scheduling Operations .........................60
         B.1. Example: "Organizer" Inviting Multiple "Attendees" .........61
         B.2. Example: "Attendee" Receiving an Invitation ................63
         B.3. Example: "Attendee" Replying to an Invitation ..............64
         B.4. Example: "Organizer" Receiving a Reply to an Invitation ....66
         B.5. Example: "Organizer" Requesting Busy Time Information ......69
         B.6. Example: User Attempting to Invite "Attendee" on
              Behalf of "Organizer" ......................................71
         B.7. Example: "Attendee" Declining an Instance of a
              Recurring Event ............................................72
         B.8. Example: "Attendee" Removing an Instance of a
              Recurring Event ............................................75

    1.  Introduction

       This document specifies extensions to the CalDAV "calendar-access"
       [RFC4791] feature to enable scheduling of iCalendar-based [RFC5545]
       calendar components between calendar users.

       This extension leverages the scheduling methods defined in the
       iCalendar Transport-independent Interoperability Protocol (iTIP)
       [RFC5546] to permit calendar users to perform scheduling operations
       such as schedule, reschedule, respond to scheduling request, or
       cancel calendar components, as well as search for busy time
       information.  However, the following iTIP [RFC5546] features are not
       covered: publishing, countering, delegating, refreshing, and
       forwarding calendar components, as well as replacing the "Organizer"
       of a calendar component.  It is expected that future extensions will
       be developed to address these.

       This specification defines a client/server scheduling protocol, where
       the server is made responsible for sending scheduling messages and
       processing incoming scheduling messages.  The client operations of
       creating, modifying, or deleting a calendar component in a calendar
       are enough to trigger the server to deliver the necessary scheduling
       messages to the appropriate calendar users.  This approach is
       sometimes referred to as "implicit scheduling".

       This specification only addresses how scheduling occurs with users on
       a single system (i.e., scheduling between CalDAV servers, or some
       other calendaring and scheduling system, is not defined).  However,
       this specification is compatible with servers being able to send or
       receive scheduling messages with "external" users (e.g., using the
       iCalendar Message-Based Interoperability Protocol (iMIP) [RFC6047]).

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    RFC 6638                    CalDAV Scheduling                  June 2012

       Section 3 defines the automated "Scheduling Operations" that allow a
       client to store iCalendar data on a CalDAV server, with the server
       taking specific actions in response.  One of three scheduling
       operations can take place -- "create", "modify", or "remove", based
       on the HTTP method used for the request -- in addition to a
       comparison between any existing and any new iCalendar data.

       Section 4 defines how the server processes scheduling messages sent
       as the result of a scheduling operation.

       Section 5 defines how freebusy requests with an immediate response
       are accomplished.

       Section 6 defines access control privileges for the scheduling
       operations defined in this specification.

       For the majority of the following discussion, scheduling of events
       will be discussed.  However, scheduling of to-dos is also fully
       supported by this specification.

       This specification has been under development for a number of years,
       and most current implementations of CalDAV support it.  With the
       publication of this document, it is expected that all new CalDAV
       implementations will support it by default.  Interoperability tests
       have been performed regularly.  Significant issues with incompatible
       CalDAV implementations are not anticipated.

    1.1.  Terminology

       This specification reuses much of the same terminology as iCalendar
       [RFC5545], iTIP [RFC5546], WebDAV [RFC4918], and CalDAV [RFC4791].
       Additional terms used by this specification are as follows:

       Scheduling object resource:  A calendar object resource contained in
          a calendar collection for which the server will take care of
          sending scheduling messages on behalf of the owner of the calendar
          collection.

       Organizer scheduling object resource:  A scheduling object resource
          owned by the "Organizer".

       Attendee scheduling object resource:  A scheduling object resource
          owned by an "Attendee".

       Scheduling operation:  Add, change, or remove operations on a
          scheduling object resource for which the server will deliver
          scheduling messages to other calendar users.

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       Scheduling message:  A calendar object that describes a scheduling
          operation such as schedule, reschedule, reply, or cancel.

       Scheduling Outbox collection:  A resource at which busy time
          information requests are targeted.

       Scheduling Inbox collection:  A collection in which incoming
          scheduling messages are delivered.

    1.2.  Notational Conventions

       The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
       "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
       document are to be interpreted as described in [RFC2119].

       The Augmented BNF (ABNF) syntax used by this document to specify the
       format definition of new iCalendar elements is defined in [RFC5234].

       The ABNF syntax used by this document to specify the format
       definition of new message header fields to be used with the HTTP/1.1
       protocol is described in Section 2.1 of [RFC2616].  Since this
       Augmented BNF uses the basic production rules provided in Section 2.2
       of [RFC2616], these rules apply to this document as well.

       The term "protected" is used in the Conformance field of WebDAV
       property definitions as defined in Section 15 of [RFC4918].

       Calendaring and scheduling roles are referred to in quoted-strings of
       text with the first character of each word in uppercase.  For
       example, "Organizer" refers to a role of a calendar user within the
       scheduling protocol defined by [RFC5546].

    1.3.  XML Namespaces and Processing

       This document uses XML DTD fragments ([W3C.REC-xml-20081126],
       Section 3.2) as a purely notational convention.  WebDAV request and
       response bodies cannot be validated by a DTD due to the specific
       extensibility rules defined in Section 17 of [RFC4918] and due to the
       fact that all XML elements defined by that specification use the XML
       namespace name "DAV:".  In particular,

       1.  element names use the "DAV:" namespace,

       2.  element ordering is irrelevant unless explicitly stated,

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       3.  extension elements (elements not already defined as valid child
           elements) can be added anywhere, except when explicitly stated
           otherwise, and

       4.  extension attributes (attributes not already defined as valid for
           this element) can be added anywhere, except when explicitly
           stated otherwise.

       The XML elements specified in this document are defined in the
       "urn:ietf:params:xml:ns:caldav" XML namespace registered by CalDAV
       [RFC4791].

       When XML element types in the namespaces "DAV:" and
       "urn:ietf:params:xml:ns:caldav" are referenced in this document
       outside of the context of an XML fragment, the strings "DAV:" and
       "CALDAV:" will be prefixed to the element types, respectively.

       This document inherits, and sometimes extends, DTD productions from
       Section 14 of [RFC4918].

       Also note that some CalDAV XML element names are identical to WebDAV
       XML element names, though their namespace differs.  Care needs to be
       taken not to confuse the two sets of names.

    2.  Scheduling Support

       A server that supports the features described in this document is
       REQUIRED to support the CalDAV "calendar-access" [RFC4791] feature.
       Servers include "calendar-auto-schedule" as a field in the DAV
       response header from an OPTIONS request on any resource that supports
       any scheduling operations, properties, privileges, or methods.

       This specification introduces new collection resource types that are
       used to manage scheduling object resources, and scheduling privileges
       (as per Section 6), as well as provide scheduling functionality.  It
       is the server's responsibility to create these collection resources,
       and clients have no way to create or delete them.

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    2.1.  Scheduling Outbox Collection

       A scheduling Outbox collection is used as the target for busy time
       information requests, and to manage privileges that apply to outgoing
       scheduling requests.

       A scheduling Outbox collection MUST report the DAV:collection and
       CALDAV:schedule-outbox XML elements in the value of the DAV:
       resourcetype property.  The element type declaration for CALDAV:
       schedule-outbox is

         <!ELEMENT schedule-outbox EMPTY>

       Example:

         <D:resourcetype xmlns:D="DAV:">
           <D:collection/>
           <C:schedule-outbox xmlns:C="urn:ietf:params:xml:ns:caldav"/>
         </D:resourcetype>

       A scheduling Outbox collection MUST NOT be a child (at any depth) of
       a calendar collection resource.

       The following WebDAV properties specified in CalDAV "calendar-access"
       [RFC4791] MAY also be defined on scheduling Outbox collections and
       apply to scheduling messages submitted to the scheduling Outbox
       collection with the POST method:

       o  CALDAV:supported-calendar-component-set

       o  CALDAV:supported-calendar-data

       o  CALDAV:max-resource-size

       o  CALDAV:min-date-time

       o  CALDAV:max-date-time

       o  CALDAV:max-attendees-per-instance

       The use of child resources in a scheduling Outbox collection is
       reserved for future revisions or extensions of this specification.

       The following WebDAV property is defined on principal resources and
       used to locate the corresponding Outbox collection for the associated
       principal.

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    2.1.1.  CALDAV:schedule-outbox-URL Property

       Name:  schedule-outbox-URL

       Namespace:  urn:ietf:params:xml:ns:caldav

       Purpose:  Identify the URL of the scheduling Outbox collection owned
          by the associated principal resource.

       Protected:  This property MAY be protected.

       PROPFIND behavior:  This property SHOULD NOT be returned by a
          PROPFIND DAV:allprop request (as defined in Section 14.2 of
          [RFC4918]).

       COPY/MOVE behavior:  This property value SHOULD be preserved in COPY
          and MOVE operations.

       Description:  This property is needed for a client to determine where
          the scheduling Outbox collection of the current user is located so
          that sending of scheduling messages can occur.  If not present,
          then the associated calendar user is not enabled for the sending
          of scheduling messages on the server.

       Definition:

         <!ELEMENT schedule-outbox-URL (DAV:href)>

    2.2.  Scheduling Inbox Collection

       A scheduling Inbox collection contains copies of incoming scheduling
       messages.  These can be requests sent by an "Organizer", or replies
       sent by an "Attendee" in response to a request.  The scheduling Inbox
       collection is also used to manage scheduling privileges.

       A scheduling Inbox collection MUST report the DAV:collection and
       CALDAV:schedule-inbox XML elements in the value of the DAV:
       resourcetype property.  The element type declaration for CALDAV:
       schedule-inbox is

         <!ELEMENT schedule-inbox EMPTY>

       Example:

         <D:resourcetype xmlns:D="DAV:">
           <D:collection/>
           <C:schedule-inbox xmlns:C="urn:ietf:params:xml:ns:caldav"/>
         </D:resourcetype>

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       Scheduling Inbox collections MUST only contain calendar object
       resources that obey the restrictions specified in iTIP [RFC5546].
       Consequently, scheduling Inbox collections MUST NOT contain any types
       of collection resources.  Restrictions defined in Section 4.1 of
       CalDAV "calendar-access" [RFC4791] on calendar object resources
       contained in calendar collections (e.g., Unique Identifier ("UID")
       uniqueness) do not apply to calendar object resources contained in a
       scheduling Inbox collection.  Thus, multiple calendar object
       resources contained in a scheduling Inbox collection can have the
       same "UID" property value (i.e., multiple scheduling messages for the
       same calendar component).

       A scheduling Inbox collection MUST NOT be a child (at any depth) of a
       calendar collection resource.

       The following WebDAV properties specified in CalDAV "calendar-access"
       [RFC4791] MAY also be defined on scheduling Inbox collections and
       apply to scheduling messages delivered to the collection:

       o  CALDAV:supported-calendar-component-set

       o  CALDAV:supported-calendar-data

       o  CALDAV:max-resource-size

       o  CALDAV:min-date-time

       o  CALDAV:max-date-time

       o  CALDAV:max-instances

       o  CALDAV:max-attendees-per-instance

       o  CALDAV:calendar-timezone

       The following WebDAV property is defined on principal resources and
       used to locate the corresponding Inbox collection for the associated
       principal.

    2.2.1.  CALDAV:schedule-inbox-URL Property

       Name:  schedule-inbox-URL

       Namespace:  urn:ietf:params:xml:ns:caldav

       Purpose:  Identify the URL of the scheduling Inbox collection owned
          by the associated principal resource.

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       Protected:  This property MAY be protected.

       PROPFIND behavior:  This property SHOULD NOT be returned by a
          PROPFIND DAV:allprop request (as defined in Section 14.2 of
          [RFC4918]).

       COPY/MOVE behavior:  This property value SHOULD be preserved in COPY
          and MOVE operations.

       Description:  This property allows a client to determine where the
          scheduling Inbox collection of the current user is located so that
          processing of scheduling messages can occur.  If not present, then
          the associated calendar user is not enabled for reception of
          scheduling messages on the server.

       Definition:

         <!ELEMENT schedule-inbox-URL (DAV:href)>

    2.3.  Calendaring Reports Extensions

       This specification extends the CALDAV:calendar-query and CALDAV:
       calendar-multiget REPORTs to return results for calendar object
       resources in scheduling Inbox collections.

       When a CALDAV:calendar-query REPORT includes a time-range query and
       targets a scheduling Inbox collection, if any calendar object
       resources contain "VEVENT" calendar components that do not include a
       "DTSTART" iCalendar property (as allowed by iTIP [RFC5546]) then such
       components MUST always match the time-range query test.

       Note that the CALDAV:free-busy-query REPORT is not supported on
       scheduling Inbox collections.

    2.4.  Additional Principal Properties

       This section defines new properties for WebDAV principal resources as
       defined in [RFC3744].  These properties are likely to be protected,
       but the server MAY allow them to be written by appropriate users.

    2.4.1.  CALDAV:calendar-user-address-set Property

       Name:  calendar-user-address-set

       Namespace:  urn:ietf:params:xml:ns:caldav

       Purpose:  Identify the calendar addresses of the associated principal
          resource.

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       Protected:  This property MAY be protected.

       PROPFIND behavior:  This property SHOULD NOT be returned by a
          PROPFIND DAV:allprop request (as defined in Section 14.2 of
          [RFC4918]).

       COPY/MOVE behavior:  This property value SHOULD be preserved in COPY
          and MOVE operations.

       Description:  Support for this property is REQUIRED.  This property
          is needed to map calendar user addresses in iCalendar data to
          principal resources and their associated scheduling Inbox and
          Outbox collections.  In the event that a user has no well-defined
          identifier for his calendar user address, the URI of his principal
          resource can be used.  This property SHOULD be searchable using
          the DAV:principal-property-search REPORT.  The DAV:principal-
          search-property-set REPORT SHOULD identify this property as such.
          If not present, then the associated calendar user is not enabled
          for scheduling on the server.

       Definition:

         <!ELEMENT calendar-user-address-set (DAV:href*)>

       Example:

         <C:calendar-user-address-set xmlns:D="DAV:"
             xmlns:C="urn:ietf:params:xml:ns:caldav">
           <D:href>mailto:bernard@example.com</D:href>
           <D:href>mailto:bernard.desruisseaux@example.com</D:href>
         </C:calendar-user-address-set>

    2.4.2.  CALDAV:calendar-user-type Property

       Name:  calendar-user-type

       Namespace:  urn:ietf:params:xml:ns:caldav

       Purpose:  Identifies the calendar user type of the associated
          principal resource.

       Value:  Same values allowed for the iCalendar "CUTYPE" property
          parameter defined in Section 3.2.3 of [RFC5545].

       Protected:  This property MAY be protected.

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       PROPFIND behavior:  This property SHOULD NOT be returned by a
          PROPFIND DAV:allprop request (as defined in Section 14.2 of
          [RFC4918]).

       COPY/MOVE behavior:  This property value SHOULD be preserved in COPY
          and MOVE operations.

       Description:  Clients can query principal resources in order to look
          up "Attendees" available on the server.  When doing this, it is
          useful to know, or restrict the query to, certain types of
          calendar users (e.g., only search for "people", or only search for
          "rooms").  This property MAY be defined on principal resources to
          indicate the type of calendar user associated with the principal
          resource.  Its value is the same as the iCalendar "CUTYPE"
          property parameter that can be used on "ATTENDEE" properties.
          This property SHOULD be searchable using the DAV:principal-
          property-search REPORT.  The DAV:principal-search-property-set
          REPORT SHOULD identify this property as such.

       Definition:

         <!ELEMENT calendar-user-type (#PCDATA)>

       Example:

         <C:calendar-user-type
             xmlns:C="urn:ietf:params:xml:ns:caldav">INDIVIDUAL<
         /C:calendar-user-type>

    3.  Scheduling Operations

       When a calendar object resource is created, modified, or removed from
       a calendar collection, the server examines the calendar data and
       checks to see whether the data represents a scheduling object
       resource.  If it does, the server will automatically attempt to
       deliver a scheduling message to the appropriate calendar users.
       Several types of scheduling operations can occur in this case,
       equivalent to iTIP "REQUEST", "REPLY", "CANCEL", and "ADD"
       operations.

    3.1.  Identifying Scheduling Object Resources

       Calendar object resources on which the server performs scheduling
       operations are referred to as scheduling object resources.  There are
       two types of scheduling object resources: organizer scheduling object
       resources, and attendee scheduling object resources.

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       A calendar object resource is considered to be a valid organizer
       scheduling object resource if the "ORGANIZER" iCalendar property is
       present and set in all the calendar components to a value that
       matches one of the calendar user addresses of the owner of the
       calendar collection.

       A calendar object resource is considered to be a valid attendee
       scheduling object resource if the "ORGANIZER" iCalendar property is
       present and set in all the calendar components to the same value and
       doesn't match one of the calendar user addresses of the owner of the
       calendar collection, and if at least one of the "ATTENDEE" iCalendar
       property values matches one of the calendar user addresses of the
       owner of the calendar collection.

       The creation of attendee scheduling object resources is typically
       done by the server, with the resource being created in an appropriate
       calendar collection (see Section 4.3).

    3.2.  Handling Scheduling Object Resources

       The server's behavior when processing a scheduling object resource
       depends on whether it is owned by the "Organizer" or an "Attendee"
       specified in the calendar data.

    3.2.1.  Organizer Scheduling Object Resources

       An "Organizer" can create, modify, or remove a scheduling object
       resource, subject to access privileges, preconditions, and the
       restrictions defined in Section 4.1 of [RFC4791].  These operations
       are each described next, and how they are invoked via HTTP requests
       is described in Section 3.2.3.

       The "Organizer" of a calendar component can also be an "Attendee" of
       that calendar component.  In such cases, the server MUST NOT send a
       scheduling message to the "Attendee" that matches the "Organizer".

       The server SHOULD reject any attempt to set the "PARTSTAT" iCalendar
       property parameter value of the "ATTENDEE" iCalendar property of
       other users in the calendar object resource to a value other than
       "NEEDS-ACTION" if the "SCHEDULE-AGENT" property parameter value is
       not present or set to the value "SERVER".

       The server MAY reject attempts to create a scheduling object resource
       that specifies a "UID" property value already specified in a
       scheduling object resource contained in another calendar collection
       of the "Organizer".

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    3.2.1.1.  Create

       When an "Organizer" creates a scheduling object resource, the server
       MUST inspect each "ATTENDEE" property to determine whether to send a
       scheduling message.  The table below indicates the appropriate iTIP
       method used by the server, taking into account any "SCHEDULE-AGENT"
       property parameter (see Section 7.1) specified on each "ATTENDEE"
       property.

                        +------------------+-------------+
                        | SCHEDULE-AGENT   | iTIP METHOD |
                        +------------------+-------------+
                        | SERVER (default) | REQUEST     |
                        |                  |             |
                        | CLIENT           | --          |
                        |                  |             |
                        | NONE             | --          |
                        +------------------+-------------+

       "SCHEDULE-STATUS" iCalendar property parameters are added or changed
       on "ATTENDEE" iCalendar properties in the scheduling object resource
       being created as described in Section 7.3, with the value set as
       described in Section 3.2.9.  This will result in the created calendar
       object resource differing from the calendar data sent in the HTTP
       request.  As a result, clients MAY reload the calendar data from the
       server in order to update to the new server-generated state
       information.

       The server MUST add a "SCHEDULE-STATUS" iCalendar property parameter
       (see Section 7.3) to the "ATTENDEE" iCalendar property in the
       scheduling object resource being created, and set its value as
       described in Section 3.2.9.  This will result in the created calendar
       object resource differing from the calendar data sent in the HTTP
       request.  As a result, clients MAY reload the calendar data from the
       server in order to update to the new server-generated state
       information.  Servers MUST NOT set the "SCHEDULE-STATUS" property
       parameter on the "ATTENDEE" property of "Attendees" for which it did
       not attempt to deliver a scheduling message.

       The server MUST return an error with the CALDAV:allowed-organizer-
       scheduling-object-change precondition code (Section 3.2.4.3) when the
       "Organizer" attempts to change the iCalendar data in a manner that is
       forbidden.

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    3.2.1.2.  Modify

       When an "Organizer" modifies a scheduling object resource, the server
       MUST inspect each "ATTENDEE" property in both the original and
       modified iCalendar data on a per-instance basis to determine whether
       to send a scheduling message.  The table below indicates the
       appropriate iTIP method used by the server, taking into account any
       "SCHEDULE-AGENT" property parameter (see Section 7.1) specified on
       each "ATTENDEE" property.  The values "SERVER", "CLIENT", and "NONE"
       in the top and left titles of the table refer to the "SCHEDULE-AGENT"
       parameter value of the "ATTENDEE" property, and the values "<Absent>"
       and "<Removed>" are used to cover the cases where the "ATTENDEE"
       property is not present (Original) or is being removed (Modified).

       +---------------+-----------------------------------------------+
       |               |                   Modified                    |
       |               +-----------+-----------+-----------+-----------+
       |               | <Removed> | SERVER    | CLIENT    | NONE      |
       |               |           | (default) |           |           |
       +===+===========+===========+===========+===========+===========+
       |   | <Absent>  |  --       | REQUEST / | --        | --        |
       | O |           |           | ADD       |           |           |
       | r +-----------+-----------+-----------+-----------+-----------+
       | i | SERVER    |  CANCEL   | REQUEST   | CANCEL    | CANCEL    |
       | g | (default) |           |           |           |           |
       | i +-----------+-----------+-----------+-----------+-----------+
       | n | CLIENT    |  --       | REQUEST / | --        | --        |
       | a |           |           | ADD       |           |           |
       | l +-----------+-----------+-----------+-----------+-----------+
       |   | NONE      |  --       | REQUEST / | --        | --        |
       |   |           |           | ADD       |           |           |
       +---+-----------+-----------+-----------+-----------+-----------+

       "SCHEDULE-STATUS" iCalendar property parameters are added or changed
       on "ATTENDEE" iCalendar properties in the scheduling object resource
       being modified as described in Section 7.3, with the value set as
       described in Section 3.2.9.  This will result in the created calendar
       object resource differing from the calendar data sent in the HTTP
       request.  As a result, clients MAY reload the calendar data from the
       server in order to update to the new server-generated state
       information.

       The server MUST return an error with the CALDAV:allowed-organizer-
       scheduling-object-change precondition code (Section 3.2.4.3) when the
       "Organizer" attempts to change the iCalendar data in a manner that is
       forbidden.

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    3.2.1.3.  Remove

       When an "Organizer" removes a scheduling object resource, the server
       MUST inspect each "ATTENDEE" property to determine whether to send a
       scheduling message.  The table below indicates the appropriate iTIP
       method used by the server, taking into account any "SCHEDULE-AGENT"
       property parameter (see Section 7.1) specified on each "ATTENDEE"
       property.

                        +------------------+-------------+
                        | SCHEDULE-AGENT   | iTIP METHOD |
                        +------------------+-------------+
                        | SERVER (default) | CANCEL      |
                        |                  |             |
                        | CLIENT           | --          |
                        |                  |             |
                        | NONE             | --          |
                        +------------------+-------------+

    3.2.2.  Attendee Scheduling Object Resources

       An "Attendee" can create, modify, or remove a scheduling object
       resource.  These operations are each described next, and how they are
       invoked via HTTP requests is described in Section 3.2.3.

    3.2.2.1.  Allowed "Attendee" Changes

       "Attendees" are allowed to make some changes to a scheduling object
       resource, though key properties such as start time, end time,
       location, and summary are typically under the control of the
       "Organizer".

       Servers MUST allow "Attendees" to make the following iCalendar data
       changes, subject to other restrictions, such as access privileges and
       preconditions:

       1.   change their own "PARTSTAT" iCalendar property parameter value.

       2.   add, modify, or remove any "TRANSP" iCalendar properties.

       3.   add, modify, or remove any "PERCENT-COMPLETE" iCalendar
            properties.

       4.   add, modify, or remove any "COMPLETED" iCalendar properties.

       5.   add, modify, or remove any "VALARM" iCalendar components.

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       6.   add, modify, or remove the "CALSCALE" iCalendar property within
            the top-level "VCALENDAR" component.

       7.   modify the "PRODID" iCalendar property within the top-level
            "VCALENDAR" component.

       8.   add "EXDATE" iCalendar properties and possibly remove components
            for overridden recurrence instances.

       9.   add, modify, or remove any "CREATED", "DTSTAMP", and
            "LAST-MODIFIED" iCalendar properties.

       10.  add, modify, or remove "SCHEDULE-STATUS" iCalendar property
            parameters on "ATTENDEE" properties that have a "SCHEDULE-AGENT"
            parameter set to "CLIENT".

       11.  add new components to represent overridden recurrence instances,
            provided the only changes to the recurrence instance follow the
            rules above.

       The server MUST return an error with the CALDAV:allowed-attendee-
       scheduling-object-change precondition code (Section 3.2.4.4) when the
       "Attendee" attempts to change the iCalendar data in a manner
       forbidden by the server.

    3.2.2.2.  Create

       Typically, an "Attendee" does not create scheduling object resources,
       as scheduling messages delivered to him on the server are
       automatically processed by the server and placed on one of his
       calendars (see Section 4).  However, in some cases, a scheduling
       message can get delivered directly to the client (e.g., via email
       [RFC6047]), and the "Attendee" might wish to store that on the
       server.  In that case, the client creates a scheduling object
       resource in a calendar belonging to the "Attendee".  It can then set
       the "SCHEDULE-AGENT" iCalendar property parameter on all "ORGANIZER"
       iCalendar properties in the resource to determine how the server
       treats the resource.  The value of the "SCHEDULE-AGENT" iCalendar
       property parameter on all "ORGANIZER" iCalendar properties MUST be
       the same.

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       +----------------+--------------------------------------------------+
       | SCHEDULE-AGENT | Action                                           |
       +----------------+--------------------------------------------------+
       | SERVER         | The server will attempt to process changes to    |
       | (default)      | the resource using the normal rules for attendee |
       |                | scheduling object resources.                     |
       |                |                                                  |
       | CLIENT         | The server does no special processing of the     |
       |                | resource.  The client is assumed to be handling  |
       |                | "Attendee" replies, etc.                         |
       |                |                                                  |
       | NONE           | The server does no special processing of the     |
       |                | resource.                                        |
       +----------------+--------------------------------------------------+

       "SCHEDULE-STATUS" iCalendar property parameters are added or changed
       on "ORGANIZER" iCalendar properties in the scheduling object resource
       being created as described in Section 7.3, with the value set as
       described in Section 3.2.9.

    3.2.2.3.  Modify

       When a scheduling object resource is modified by an "Attendee", the
       server's behavior depends on the value of the "SCHEDULE-AGENT"
       iCalendar property parameter on the "ORGANIZER" iCalendar properties:

       +----------------+--------------------------------------------------+
       | SCHEDULE-AGENT | Action                                           |
       +----------------+--------------------------------------------------+
       | SERVER         | The server will attempt to process the update    |
       | (default)      | using the behavior listed below.                 |
       |                |                                                  |
       | CLIENT         | The server does no special processing of the     |
       |                | resource.  The client is assumed to be handling  |
       |                | any "Attendee" replies, etc.                     |
       |                |                                                  |
       | NONE           | The server does no special processing of the     |
       |                | resource.                                        |
       +----------------+--------------------------------------------------+

       The server will inspect the changes by comparing the new scheduling
       object resource with the existing scheduling object resource.

       If the "Attendee" changes one or more "PARTSTAT" iCalendar property
       values on any component, or adds an overridden component with a
       changed "PARTSTAT" property, then the server MUST deliver an iTIP
       "REPLY" scheduling message to the "Organizer" to indicate the new
       participation status of the "Attendee".

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       If the "Attendee" adds an "EXDATE" property value to effectively
       remove a recurrence instance, the server MUST deliver an iTIP "REPLY"
       scheduling message to the "Organizer" to indicate that the "Attendee"
       has declined the instance.

       "SCHEDULE-STATUS" iCalendar property parameters are added or changed
       on "ORGANIZER" iCalendar properties in the scheduling object resource
       being modified as described in Section 7.3, with the value set as
       described in Section 3.2.9.  This will result in the updated calendar
       object resource differing from the calendar data sent in the HTTP
       request.  As a result, clients MAY reload the calendar data from the
       server in order to update to the new server-generated state
       information.

    3.2.2.4.  Remove

       When a scheduling object resource is removed by an "Attendee", the
       server's behavior depends on the value of the "SCHEDULE-AGENT"
       iCalendar property parameter on the "ORGANIZER" iCalendar properties:

       +----------------+--------------------------------------------------+
       | SCHEDULE-AGENT | Action                                           |
       +----------------+--------------------------------------------------+
       | SERVER         | The server will attempt to process the removal,  |
       | (default)      | taking into account any "Schedule-Reply" request |
       |                | header as per Section 8.1.                       |
       |                |                                                  |
       | CLIENT         | The server does no special processing of the     |
       |                | resource.  The client is assumed to be handling  |
       |                | any "Attendee" replies, etc.                     |
       |                |                                                  |
       | NONE           | The server does no special processing of the     |
       |                | resource.                                        |
       +----------------+--------------------------------------------------+

    3.2.3.  HTTP Methods

       This section describes how the use of various HTTP [RFC2616] and
       WebDAV [RFC4918] methods on a scheduling object resource will cause a
       create, modify, or remove operation on that resource as described
       above.  The use of these methods is subject to the restrictions in
       [RFC4791], in addition to what is described below.

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    3.2.3.1.  PUT

       When the server receives a PUT method request, it MUST execute the
       following operations, provided all appropriate preconditions are met:

       +------------------------+--------------------------+---------------+
       | Existing Destination   | Resulting Destination    | Server        |
       | Resource               | Resource                 | Operation     |
       +------------------------+--------------------------+---------------+
       | None                   | Calendar object resource | None          |
       |                        |                          |               |
       | None                   | Scheduling object        | Create        |
       |                        | resource                 |               |
       |                        |                          |               |
       | Calendar object        | Calendar object resource | None          |
       | resource               |                          |               |
       |                        |                          |               |
       | Calendar object        | Scheduling object        | Create        |
       | resource               | resource                 |               |
       | Scheduling object      | Calendar object resource | Remove        |
       | resource               |                          |               |
       |                        |                          |               |
       | Scheduling object      | Scheduling object        | Modify        |
       | resource               | resource                 |               |
       +------------------------+--------------------------+---------------+

    3.2.3.2.  DELETE

       When the server receives a DELETE method request targeted at a
       scheduling object resource, it MUST execute the Remove operation.

       When the server receives a DELETE method request targeted at a
       calendar collection, it MUST execute the Remove operation on all
       scheduling object resources contained in the calendar collection.

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    3.2.3.3.  COPY

       When the server receives a COPY method request, it MUST execute the
       following operations based on the source and destination collections
       in the request:

       +-----------------------+------------------------+------------------+
       | Source Collection     | Destination Collection | Server Operation |
       +-----------------------+------------------------+------------------+
       | Non-calendar          | Non-calendar           | None             |
       | collection            | collection             |                  |
       |                       |                        |                  |
       | Non-calendar          | Calendar collection    | (1)              |
       | collection            |                        |                  |
       |                       |                        |                  |
       | Calendar collection   | Non-calendar           | None             |
       |                       | collection             |                  |
       |                       |                        |                  |
       | Calendar collection   | Calendar collection    | (2)              |
       +-----------------------+------------------------+------------------+

       Note (1):  The rules in Section 3.2.3.1 are applied for the
                  destination of the COPY request.

       Note (2):  The server MAY reject this as per Section 3.2.4.1;
                  otherwise, None.

       The behavior of a COPY method request on a calendar collection is
       undefined.

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    3.2.3.4.  MOVE

       When the server receives a MOVE method request, it MUST execute the
       following operations based on the source and destination collections
       in the request:

       +-----------------------+------------------------+------------------+
       | Source Collection     | Destination Collection | Server Operation |
       +-----------------------+------------------------+------------------+
       | Non-calendar          | Non-calendar           | None             |
       | collection            | collection             |                  |
       |                       |                        |                  |
       | Non-calendar          | Calendar collection    | (1)              |
       | collection            |                        |                  |
       |                       |                        |                  |
       | Calendar collection   | Non-calendar           | (2)              |
       |                       | collection             |                  |
       |                       |                        |                  |
       | Calendar collection   | Calendar collection    | None             |
       +-----------------------+------------------------+------------------+

       Note (1):  The rules in Section 3.2.3.1 are applied for the
                  destination of the MOVE request.

       Note (2):  The rules in Section 3.2.3.2 are applied for the source of
                  the MOVE request.

       The behavior of a MOVE method request on a calendar collection is
       undefined.

    3.2.4.  Additional Method Preconditions

       This specification defines method preconditions (see Section 16 of
       WebDAV [RFC4918]), in addition to those in [RFC4791], to provide
       machine-parseable information in error responses.

    3.2.4.1.  CALDAV:unique-scheduling-object-resource Precondition

       Name:  unique-scheduling-object-resource

       Namespace:  urn:ietf:params:xml:ns:caldav

       Apply to:  PUT, COPY, and MOVE

       Use with:  403 Forbidden

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       Purpose:  (precondition) -- Servers MAY reject requests to create a
          scheduling object resource with an iCalendar "UID" property value
          already in use by another scheduling object resource owned by the
          same user in other calendar collections.  Servers SHOULD report
          the URL of the scheduling object resource that is already making
          use of the same "UID" property value in the DAV:href element.

       Definition:

         <!ELEMENT unique-scheduling-object-resource (DAV:href?)>

       Example:

         <C:unique-scheduling-object-resource xmlns:D="DAV:"
             xmlns:C="urn:ietf:params:xml:ns:caldav">
           <D:href>/home/bernard/calendars/personal/abc123.ics</D:href>
         </C:unique-scheduling-object-resource>

    3.2.4.2.  CALDAV:same-organizer-in-all-components Precondition

       Name:  same-organizer-in-all-components

       Namespace:  urn:ietf:params:xml:ns:caldav

       Apply to:  PUT, COPY, and MOVE

       Use with:  403 Forbidden

       Purpose:  (precondition) -- All the calendar components in a
          scheduling object resource MUST contain the same "ORGANIZER"
          property value when present.

       Definition:

         <!ELEMENT same-organizer-in-all-components EMPTY>

    3.2.4.3.  CALDAV:allowed-organizer-scheduling-object-change Precondition

       Name:  allowed-organizer-scheduling-object-change

       Namespace:  urn:ietf:params:xml:ns:caldav

       Apply to:  PUT, COPY, and MOVE

       Use with:  403 Forbidden

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       Purpose:  (precondition) -- Servers MAY impose restrictions on
          modifications allowed by an "Organizer".  For instance, servers
          MAY prevent the "Organizer" from setting the "PARTSTAT" property
          parameter to a value other than "NEEDS-ACTION" if the
          corresponding "ATTENDEE" property has the "SCHEDULE-AGENT"
          property parameter set to "SERVER", or does not have the
          "SCHEDULE-AGENT" property parameter.  See Section 3.2.1.

       Definition:

         <!ELEMENT allowed-organizer-scheduling-object-change EMPTY>

    3.2.4.4.  CALDAV:allowed-attendee-scheduling-object-change Precondition

       Name:  allowed-attendee-scheduling-object-change

       Namespace:  urn:ietf:params:xml:ns:caldav

       Apply to:  PUT, COPY, and MOVE

       Use with:  403 Forbidden

       Purpose:  (precondition) -- Servers MAY impose restrictions on
          modifications allowed by an "Attendee", subject to the allowed
          changes specified in Section 3.2.2.1.

       Definition:

         <!ELEMENT allowed-attendee-scheduling-object-change EMPTY>

    3.2.5.  DTSTAMP and SEQUENCE Properties

       The server MUST ensure that a "DTSTAMP" iCalendar property is present
       and set the value to the UTC time that the scheduling message was
       generated (as required by iCalendar).

       The server MUST ensure that for each type of scheduling operation,
       the "SEQUENCE" iCalendar property value is updated as per iTIP
       [RFC5546].

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    3.2.6.  Restrict Recurrence Instances Sent to "Attendees"

       Servers MUST ensure that "Attendees" only get information about
       recurrence instances that explicitly include them as an "Attendee",
       when delivering scheduling messages for recurring calendar
       components.

       For example, if an "Attendee" is invited to only a single instance of
       a recurring event, the organizer scheduling object resource will
       contain an overridden instance in the form of a separate calendar
       component.  That separate calendar component will include the
       "ATTENDEE" property referencing the "one-off" "Attendee".  That
       "Attendee" will not be listed in any other calendar components in the
       scheduling object resource.  Any scheduling messages delivered to the
       "Attendee" will only contain information about this overridden
       instance.

       As another example, an "Attendee" could be excluded from one instance
       of a recurring event.  In that case, the organizer scheduling object
       resource will include an overridden instance with an "ATTENDEE" list
       that does not include the "Attendee" being excluded.  Any scheduling
       messages delivered to the "Attendee" will not specify the overridden
       instance but rather will include an "EXDATE" property in the "master"
       component that defines the recurrence set.

    3.2.7.  Forcing the Server to Send a Scheduling Message

       The iCalendar property parameter "SCHEDULE-FORCE-SEND", defined in
       Section 7.2, can be used by a calendar user to force the server to
       send a scheduling message to an "Attendee" or the "Organizer" in a
       situation where the server would not normally send a scheduling
       message.  For instance, an "Organizer" could use this property
       parameter to request an "Attendee" that previously declined an
       invitation to reconsider his participation status without being
       forced to modify the event.

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    3.2.8.  "Attendee" Participation Status

       This section specifies additional requirements on the handling of the
       "PARTSTAT" property parameter when the "SCHEDULE-AGENT" property
       parameter on the corresponding "ATTENDEE" property is set to the
       value "SERVER" or is not present.

       A reschedule occurs when any "DTSTART", "DTEND", "DURATION", "DUE",
       "RRULE", "RDATE", or "EXDATE" property changes in a calendar
       component such that existing recurrence instances are impacted by the
       changes, as shown in the table below.  Servers MUST reset the
       "PARTSTAT" property parameter value of all "ATTENDEE" properties,
       except the one that corresponds to the "Organizer", to "NEEDS-ACTION"
       for each calendar component change that causes any instance to be
       rescheduled.

       +-----------+-------------------------------------------------------+
       | Property  | Server Action                                         |
       +-----------+-------------------------------------------------------+
       | DTSTART,  | Any change to these properties results in "PARTSTAT"  |
       | DTEND,    | being set to "NEEDS-ACTION".                          |
       | DURATION, |                                                       |
       | DUE       |                                                       |
       |           |                                                       |
       | RRULE     | A change to or addition of this property that results |
       |           | in the addition of new recurring instances or a       |
       |           | change in time for existing recurring instances       |
       |           | results in "PARTSTAT" being reset to "NEEDS-ACTION"   |
       |           | on each affected component.                           |
       |           |                                                       |
       | RDATE     | A change to or addition of this property that results |
       |           | in the addition of new recurring instances or a       |
       |           | change in time for existing recurring instances       |
       |           | results in "PARTSTAT" being reset to "NEEDS-ACTION"   |
       |           | on each affected component.                           |
       |           |                                                       |
       | EXDATE    | A change to or removal of this property that results  |
       |           | in the reinstatement of recurring instances results   |
       |           | in "PARTSTAT" being set to "NEEDS-ACTION" on each     |
       |           | affected component.                                   |
       +-----------+-------------------------------------------------------+

       The server MAY allow the "Organizer's" client to change an
       "Attendee's" "PARTSTAT" property parameter value to "NEEDS-ACTION" at
       any other time (e.g., when the "LOCATION" property value changes, an
       "Organizer" might wish to re-invite "Attendees" who might be impacted
       by the change).

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    3.2.9.  Schedule Status Values

       When scheduling with an "Attendee", there are two types of status
       information that can be returned during the operation.  The first
       type of status information is a "delivery" status that indicates
       whether the scheduling message from the "Organizer" to the "Attendee"
       was delivered or not, or what the current status of delivery is.  The
       second type of status information is a "reply" status corresponding
       to the "Attendee's" own "REQUEST-STATUS" information from the
       scheduling message reply that is sent back to the "Organizer".

       Similarly, when an "Attendee" sends a reply back to the "Organizer",
       there will be "delivery" status information for the scheduling
       message sent to the "Organizer".  However, there is no
       "REQUEST-STATUS" sent back by the "Organizer", so there is no
       equivalent of the "reply" status as per scheduling messages to
       "Attendees".

       The "delivery" status information on an "ORGANIZER" or "ATTENDEE"
       iCalendar property is conveyed in the "SCHEDULE-STATUS" property
       parameter value (Section 7.3).  The status code value for "delivery"
       status can be one of the following:

       +----------+--------------------------------------------------------+
       | Delivery | Description                                            |
       | Status   |                                                        |
       | Code     |                                                        |
       +----------+--------------------------------------------------------+
       | 1.0      | The scheduling message is pending.  That is, the       |
       |          | server is still in the process of sending the message. |
       |          | The status code value can be expected to change once   |
       |          | the server has completed its sending and delivery      |
       |          | attempts.                                              |
       |          |                                                        |
       | 1.1      | The scheduling message has been successfully sent.     |
       |          | However, the server does not have explicit information |
       |          | about whether the scheduling message was successfully  |
       |          | delivered to the recipient.  This state can occur with |
       |          | "store and forward" style scheduling protocols such as |
       |          | iMIP [RFC6047] (iTIP using email).                     |
       |          |                                                        |
       | 1.2      | The scheduling message has been successfully           |
       |          | delivered.                                             |
       |          |                                                        |

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       | 3.7      | The scheduling message was not delivered because the   |
       |          | server did not recognize the calendar user address as  |
       |          | a valid calendar user.  Note that this code applies to |
       |          | both "Organizer" and "Attendee" calendar user          |
       |          | addresses.                                             |
       |          |                                                        |
       | 3.8      | The scheduling message was not delivered due to        |
       |          | insufficient privileges.  Note that this code applies  |
       |          | to privileges granted by both the "Organizer" and      |
       |          | "Attendee" calendar users.                             |
       |          |                                                        |
       | 5.1      | The scheduling message was not delivered because the   |
       |          | server could not complete delivery of the message.     |
       |          | This is likely due to a temporary failure, and the     |
       |          | originator can try to send the message again at a      |
       |          | later time.                                            |
       |          |                                                        |
       | 5.2      | The scheduling message was not delivered because the   |
       |          | server was not able to find a way to deliver the       |
       |          | message.  This is likely a permanent failure, and the  |
       |          | originator ought not try to send the message again, at |
       |          | least without verifying/correcting the calendar user   |
       |          | address of the recipient.                              |
       |          |                                                        |
       | 5.3      | The scheduling message was not delivered and was       |
       |          | rejected because scheduling with that recipient is not |
       |          | allowed.  This is likely a permanent failure, and the  |
       |          | originator ought not try to send the message again.    |
       +----------+--------------------------------------------------------+

       The status code for "reply" status can be any of the valid iTIP
       [RFC5546] "REQUEST-STATUS" values.

       The 1.xx "REQUEST-STATUS" codes are new.  This specification modifies
       item (2) of Section 3.6 of [RFC5546] by adding the following
       restriction:

          For a 1.xx code, all components MUST have exactly the same code.

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       Definition of the new 1.xx codes is as follows:

    3.2.9.1.  Status Code 1.0

       Status Code:  1.0

       Status Description:  Pending.

       Status Exception Data:  None.

       Description:  Delivery of the iTIP message is pending.

    3.2.9.2.  Status Code 1.1

       Status Code:  1.1

       Status Description:  Sent.

       Status Exception Data:  None.

       Description:  The iTIP message has been sent, though no information
          about successful delivery is known.

    3.2.9.3.  Status Code 1.2

       Status Code:  1.2

       Status Description:  Delivered.

       Status Exception Data:  None.

       Description:  The iTIP message has been sent and delivered.

    3.2.10.  Avoiding Conflicts when Updating Scheduling Object Resources

       Scheduling object resources on the server might change frequently as
       "Attendees" change their participation status, triggering updates to
       the "Organizer", and refreshes of other "Attendees'" copies of the
       scheduling object resource.  This can lead to an "inconsequential"
       change to a calendar user's data -- one that does not directly impact
       the user's own participation status.  When this occurs, clients have
       to reload calendar data and reconcile with changes being made by
       calendar users.  To avoid the need for this, the server can instead
       merge calendar data changes from a client with changes made as a
       result of a scheduling operation carried out by some other calendar
       user.

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       This specification introduces a new WebDAV resource property CALDAV:
       schedule-tag with a corresponding response header "Schedule-Tag", and
       a new "If-Schedule-Tag-Match" request header to allow client changes
       to be appropriately merged with server changes in the case where the
       changes on the server were the result of an "inconsequential"
       scheduling message update (one that simply updates the status
       information of "Attendees" due to a reply from another "Attendee").

       Servers MUST automatically resolve conflicts with "inconsequential"
       changes done to scheduling object resources when the "If-Schedule-
       Tag-Match" request header is specified.  The If-Schedule-Tag-Match
       request header applies only to the Request-URI, and not to the
       destination of a COPY or MOVE.

       A response to any successful GET or PUT request targeting a
       scheduling object resource MUST include a Schedule-Tag response
       header with the value set to the same value as the CALDAV:schedule-
       tag WebDAV property of the resource.

       A response to any successful COPY or MOVE request that specifies a
       Destination request header targeting a scheduling object resource
       MUST include a Schedule-Tag response header with the value set to the
       same value as the CALDAV:schedule-tag WebDAV property of the
       destination resource.

       Clients SHOULD use the If-Schedule-Tag-Match header on requests that
       update scheduling object resources, instead of HTTP ETag-based
       precondition tests (e.g., If-Match).  Normal ETag-based precondition
       tests are used in all other cases, e.g., for synchronization.

       The value of the CALDAV:schedule-tag property changes according to
       these rules:

       o  For an "Organizer's" copy of a scheduling object resource:

          1.  The server MUST NOT change the CALDAV:schedule-tag property
              value when the scheduling object resource is updated as the
              result of automatically processing a scheduling message reply
              from an "Attendee".  For instance, when an "Attendee" replies
              to the "Organizer", the CALDAV:schedule-tag property is
              unchanged after the "Organizer's" scheduling object resource
              has been automatically updated by the server with the
              "Attendee's" new participation status.

          2.  The server MUST change the CALDAV:schedule-tag property value
              when the scheduling object resource is changed directly via an
              HTTP request (e.g., PUT, COPY, or MOVE).

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       o  For an "Attendee's" copy of a scheduling object resource:

          1.  The server MUST change the CALDAV:schedule-tag property value
              when the scheduling object resource is changed as the result
              of processing a scheduling message update from an "Organizer"
              that contains changes other than just the participation status
              of "Attendees".

          2.  The server MUST NOT change the CALDAV:schedule-tag property
              value when the scheduling object resource is changed as the
              result of processing a scheduling message update from an
              "Organizer" that only specifies changes in the participation
              status of "Attendees".  For instance, when "Attendee" "A"
              replies to "Organizer" "O", and "Attendee" "B" receives a
              scheduling message update from "Organizer" "O" with the new
              participation status of "Attendee" "A", the CALDAV:schedule-
              tag property of "Attendee" "B"'s scheduling object resource
              would remain the same.

          3.  The server MUST change the CALDAV:schedule-tag property value
              when the scheduling object resource is changed directly via an
              HTTP request (e.g., PUT, COPY, or MOVE).

    3.2.10.1.  PUT

       Clients MAY use the If-Schedule-Tag-Match request header to do a PUT
       request that ensures that "inconsequential" changes on the server do
       not result in a precondition error.  The value of the request header
       is set to the last Schedule-Tag value received for the resource being
       modified.  If the value of the If-Schedule-Tag-Match header matches
       the current value of the CALDAV:schedule-tag property, the server
       MUST take any "ATTENDEE" property changes for all "Attendees" other
       than the owner of the scheduling object resource and apply those to
       the new resource being stored.  Otherwise, the server MUST fail the
       request with a 412 Precondition Failed status code.

    3.2.10.2.  DELETE, COPY, or MOVE

       Clients MAY use the If-Schedule-Tag-Match request header to do a
       DELETE, COPY, or MOVE request that ensures that "inconsequential"
       changes on the server do not result in a precondition error.  The
       value of the request header is set to the last Schedule-Tag value
       received for the resource being deleted.  If the value of the
       If-Schedule-Tag-Match header matches the current value of the CALDAV:
       schedule-tag property, the server performs the normal DELETE, COPY,
       or MOVE request processing for the resource.  Otherwise, the server
       MUST fail the request with a 412 Precondition Failed status code.

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    4.  Processing Incoming Scheduling Messages

       Scheduling operations can cause the delivery of a scheduling message
       into an "Organizer's" or "Attendee's" scheduling Inbox collection.
       Servers MUST automatically process incoming scheduling messages using
       the rules defined by [RFC5546], by creating or updating the
       corresponding scheduling object resources on calendars owned by the
       owner of the scheduling Inbox collection.  In addition, the
       scheduling message is stored in the scheduling Inbox collection as an
       indicator to the client that a scheduling operation has taken place.
       Scheduling messages are typically removed from the scheduling Inbox
       collection by the client once the calendar user has acknowledged the
       change.

       The server MUST take into account privileges on the scheduling Inbox
       collection when processing incoming scheduling messages, to determine
       whether delivery of the scheduling message is allowed.  Privileges on
       calendars containing any matching scheduling object resource are not
       considered in this case (i.e., a schedule message from another user
       can cause modifications to resources in calendar collections that the
       other user would not normally have read or write access to).
       Additionally, servers MUST take into account any scheduling Inbox
       collection preconditions (see Section 2.2) when delivering the
       scheduling message, and MUST take into account the similar
       preconditions on any calendar collection that contains, or would
       contain, the corresponding scheduling object resource.

    4.1.  Processing "Organizer" Requests, Additions, and Cancellations

       For a scheduling message sent by an "Organizer", the server first
       tries to locate a corresponding scheduling object resource belonging
       to the "Attendee".  If no matching scheduling object resource exists,
       the server treats the scheduling message as a new message; otherwise,
       it is treated as an update.

       In the case of a new message, the server processes the scheduling
       message and creates a new scheduling object resource as per
       Section 4.3.

       In the case of an update, the server processes the scheduling message
       and updates the matching scheduling object resource belonging to the
       "Attendee" to reflect the changes sent by the "Organizer".

       In each case, the scheduling message MUST only appear in the
       "Attendee's" scheduling Inbox collection once all automatic
       processing has been done.

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    4.2.  Processing "Attendee" Replies

       For a scheduling message reply sent by an "Attendee", the server
       first locates the corresponding scheduling object resource belonging
       to the "Organizer".  If the corresponding scheduling object resource
       cannot be found, the server SHOULD ignore the scheduling message.

       The server MUST then update the "PARTSTAT" iCalendar property
       parameter value of each "ATTENDEE" iCalendar property in the
       scheduling object resource to match the changes indicated in the
       reply (taking into account the fact that an "Attendee" could have
       created a new overridden iCalendar component to indicate different
       participation status on one or more instances of a recurring event).

       The server MUST also update or add the "SCHEDULE-STATUS" property
       parameter on each matching "ATTENDEE" iCalendar property and set its
       value to that of the "REQUEST-STATUS" property in the reply, or to
       "2.0" if "REQUEST-STATUS" is not present (also taking into account
       recurrence instances).  If there are multiple "REQUEST-STATUS"
       properties in the reply, the "SCHEDULE-STATUS" property parameter
       value is set to a comma-separated list of status codes, one from each
       "REQUEST-STATUS" property.

       The server SHOULD send scheduling messages to all the other
       "Attendees" indicating the change in participation status of the
       "Attendee" replying, subject to the recurrence requirements of
       Section 3.2.6.

       The scheduling message MUST only appear in the "Organizer's"
       scheduling Inbox collection once all automatic processing has been
       done.

    4.3.  Default Calendar Collection

       The server processes scheduling messages received for an "Attendee"
       by creating a new scheduling object resource in a calendar collection
       belonging to the "Attendee", when one does not already exist.  A
       calendar user that is an "Attendee" in a scheduling operation MUST
       have at least one valid calendar collection available.  If there is
       no valid calendar collection, then the server MUST reject the attempt
       to deliver the scheduling message to the "Attendee".

       Servers MAY provide support for a default calendar collection -- that
       is, the calendar collection in which new scheduling object resources
       will be created.  The CALDAV:schedule-default-calendar-URL WebDAV
       property, which can be present on the scheduling Inbox collection of
       a calendar user, specifies whether this calendar user has a default
       calendar collection.  See Section 9.2.

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       Servers SHOULD create new scheduling object resources in the default
       calendar collection, if the CALDAV:schedule-default-calendar-URL
       WebDAV property is set.

       Servers MAY allow clients to change the default calendar collection
       by changing the value of the CALDAV:schedule-default-calendar-URL
       WebDAV property on the scheduling Inbox collection.  However, the
       server MUST ensure that any new value for that property refers to a
       valid calendar collection belonging to the owner of the scheduling
       Inbox collection.

       Servers MUST reject any attempt to delete the default calendar
       collection.

    4.3.1.  Additional Method Preconditions

       This specification defines additional method preconditions (see
       Section 16 of WebDAV [RFC4918]) to provide machine-parseable
       information in error responses.

    4.3.1.1.  CALDAV:default-calendar-needed Precondition

       Name:  default-calendar-needed

       Namespace:  urn:ietf:params:xml:ns:caldav

       Apply to:  DELETE

       Use with:  403 Forbidden

       Purpose:  (precondition) -- The client attempted to delete the
          calendar collection currently referenced by the CALDAV:schedule-
          default-calendar-URL property, or attempted to remove the CALDAV:
          schedule-default-calendar-URL property on the scheduling Inbox
          collection on a server that doesn't allow such operations.

       Definition:

         <!ELEMENT default-calendar-needed EMPTY>

    4.3.1.2.  CALDAV:valid-schedule-default-calendar-URL Precondition

       Name:  valid-schedule-default-calendar-URL

       Namespace:  urn:ietf:params:xml:ns:caldav

       Apply to:  PROPPATCH

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       Use with:  403 Forbidden

       Purpose:  (precondition) -- The client attempted to set the CALDAV:
          schedule-default-calendar-URL property to a DAV:href element that
          doesn't reference a valid calendar collection.  Note: Servers that
          do not allow clients to change the CALDAV:schedule-default-
          calendar-URL property would simply return the DAV:cannot-modify-
          protected-property precondition defined in Section 16 of WebDAV
          [RFC4918].

       Definition:

         <!ELEMENT valid-schedule-default-calendar-URL EMPTY>

    5.  Request for Busy Time Information

       Busy time information of one or more calendar users can be determined
       by submitting a POST request targeted at the scheduling Outbox
       collection of the calendar user requesting the information (the
       "Organizer").  To accomplish this, the request body MUST contain a
       "VFREEBUSY" calendar component with the "METHOD" iCalendar property
       set to the value "REQUEST" as specified in Section 3.3.2 of iTIP
       [RFC5546].  The resource identified by the Request-URI MUST be a
       resource collection of type CALDAV:schedule-outbox (Section 2.1).
       The "ORGANIZER" property value in the "VFREEBUSY" component MUST
       match one of the calendar user addresses of the owner of the Outbox
       collection.

       A response to a busy time request that indicates status for one or
       more calendar users MUST be an XML document with a CALDAV:schedule-
       response XML element as its root element.  This element MUST contain
       one CALDAV:response element for each calendar user, with each such
       element in turn containing elements that indicate which calendar user
       they correspond to, the scheduling status for that calendar user, any
       error codes, and an optional description.  For a successful busy time
       request, a CALDAV:calendar-data element is also present for each
       calendar user, containing the actual busy time information (i.e., an
       iCalendar "VFREEBUSY" component).  See Section 10 for details on the
       child elements.  See Appendix B.5 for an example busy time request
       and response.

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    5.1.  Status Codes

       The list below summarizes the most common status codes used for this
       method.  However, clients need to be prepared to handle other
       2/3/4/5xx series status codes as well.

          200 (OK) - The command succeeded.

          204 (No Content) - The command succeeded.

          400 (Bad Request) - The client has provided an invalid scheduling
          message.

          403 (Forbidden) - The client cannot submit a scheduling message to
          the specified Request-URI.

          404 (Not Found) - The URL in the Request-URI was not present.

          423 (Locked) - The specified resource is locked, and the client
          either is not a lock owner or the lock type requires a lock token
          to be submitted and the client did not submit it.

    5.2.  Additional Method Preconditions

       The following are existing preconditions that are reused for the POST
       method on an Outbox collection.

       o  DAV:need-privileges [RFC3744]

       o  CALDAV:supported-calendar-data [RFC4791]

       o  CALDAV:valid-calendar-data [RFC4791]

       o  CALDAV:max-resource-size [RFC4791]

       The following are new method preconditions for the POST method on an
       Outbox collection.

    5.2.1.  CALDAV:valid-scheduling-message Precondition

       Name:  valid-scheduling-message

       Namespace:  urn:ietf:params:xml:ns:caldav

       Apply to:  POST

       Use with:  400 Bad Request

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       Purpose:  (precondition) -- The resource submitted in the POST
          request MUST obey all the restrictions specified in Section 3.3.2
          of iTIP [RFC5546].

       Definition:

         <!ELEMENT valid-scheduling-message EMPTY>

    5.2.2.  CALDAV:valid-organizer Precondition

       Name:  valid-organizer

       Namespace:  urn:ietf:params:xml:ns:caldav

       Apply to:  POST

       Use with:  403 Forbidden

       Purpose:  (precondition) -- The "ORGANIZER" property value in the
          POST request's scheduling message MUST match one of the calendar
          user addresses of the owner of the scheduling Outbox collection
          being targeted by the request.

       Definition:

         <!ELEMENT valid-organizer EMPTY>

    6.  Scheduling Privileges

       New scheduling privileges are defined in this section.  All the
       scheduling privileges MUST be non-abstract and MUST appear in the
       DAV:supported-privilege-set property of scheduling Outbox and Inbox
       collections on which they are defined.

       The tables specified in Appendix A clarify which scheduling methods
       (e.g., "REQUEST", "REPLY", etc.) are controlled by each scheduling
       privilege defined in this section.

    6.1.  Privileges on Scheduling Inbox Collections

       This section defines new WebDAV Access Control List (ACL) [RFC3744]
       privileges that are defined for use on scheduling Inbox collections.
       These privileges determine whether delivery of scheduling messages
       from a calendar user is allowed by the calendar user who "owns" the
       scheduling Inbox collection.  This allows calendar users to choose
       which other calendar users can schedule with them.

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       Note that when a scheduling message is delivered to a calendar user,
       in addition to a scheduling object resource being created in the
       calendar user's scheduling Inbox collection, a new scheduling object
       resource might be created or an existing one updated in a calendar
       belonging to the calendar user.  In that case, the ability to create
       or update the scheduling object resource in the calendar is
       controlled by the privileges assigned to the scheduling Inbox
       collection.

       The privileges defined in this section are ignored if applied to a
       resource other than a scheduling Inbox collection.

    6.1.1.  CALDAV:schedule-deliver Privilege

       CALDAV:schedule-deliver is an aggregate privilege as per Section 6.3.

         <!ELEMENT schedule-deliver EMPTY>

    6.1.2.  CALDAV:schedule-deliver-invite Privilege

       The CALDAV:schedule-deliver-invite privilege controls the processing
       and delivery of scheduling messages coming from an "Organizer".

         <!ELEMENT schedule-deliver-invite EMPTY>

    6.1.3.  CALDAV:schedule-deliver-reply Privilege

       The CALDAV:schedule-deliver-reply privilege controls the processing
       and delivery of scheduling messages coming from an "Attendee".

         <!ELEMENT schedule-deliver-reply EMPTY>

    6.1.4.  CALDAV:schedule-query-freebusy Privilege

       The CALDAV:schedule-query-freebusy privilege controls freebusy
       requests targeted at the owner of the scheduling Inbox collection.

         <!ELEMENT schedule-query-freebusy EMPTY>

    6.2.  Privileges on Scheduling Outbox Collections

       This section defines new WebDAV ACL [RFC3744] privileges that are
       defined for use on scheduling Outbox collections.  These privileges
       determine which calendar users are allowed to send scheduling
       messages on behalf of the calendar user who "owns" the scheduling
       Outbox collection.  This allows calendar users to choose other
       calendar users who can act on their behalf (e.g., assistants working
       on behalf of their boss).

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       The privileges defined in this section are ignored if applied to a
       resource other than a scheduling Outbox collection.

    6.2.1.  CALDAV:schedule-send Privilege

       CALDAV:schedule-send is an aggregate privilege as per Section 6.3.

         <!ELEMENT schedule-send EMPTY>

    6.2.2.  CALDAV:schedule-send-invite Privilege

       The CALDAV:schedule-send-invite privilege controls the sending of
       scheduling messages by "Organizers".

       Users granted the DAV:bind privilege on a calendar collection, or the
       DAV:write privilege on scheduling object resources, will also need
       the CALDAV:schedule-send-invite privilege granted on the scheduling
       Outbox collection of the owner of the calendar collection or
       scheduling object resource in order to be allowed to create, modify,
       or delete scheduling object resources in a way that will trigger the
       CalDAV server to deliver scheduling messages to "Attendees".

         <!ELEMENT schedule-send-invite EMPTY>

    6.2.3.  CALDAV:schedule-send-reply Privilege

       The CALDAV:schedule-send-reply privilege controls the sending of
       scheduling messages by "Attendees".

       Users granted the DAV:bind privilege on a calendar collection, or the
       DAV:write privilege on scheduling object resources, will also need
       the CALDAV:schedule-send-reply privilege granted on the scheduling
       Outbox collection of the owner of the calendar collection or
       scheduling object resource in order to be allowed to create, modify,
       or delete scheduling object resources in a way that will trigger the
       CalDAV server to deliver scheduling message replies to the
       "Organizer".

         <!ELEMENT schedule-send-reply EMPTY>

    6.2.4.  CALDAV:schedule-send-freebusy Privilege

       The CALDAV:schedule-send-freebusy privilege controls the use of the
       POST method to submit scheduling messages that specify the scheduling
       method "REQUEST" with a "VFREEBUSY" calendar component.

         <!ELEMENT schedule-send-freebusy EMPTY>

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    6.3.  Aggregation of Scheduling Privileges

       Server implementations MUST aggregate the scheduling privileges as
       follows:

          DAV:all contains CALDAV:schedule-deliver and CALDAV:schedule-send;

          CALDAV:schedule-deliver contains CALDAV:schedule-deliver-invite,
          CALDAV:schedule-deliver-reply, and CALDAV:schedule-query-freebusy;

          CALDAV:schedule-send contains CALDAV:schedule-send-invite, CALDAV:
          schedule-send-reply, and CALDAV:schedule-send-freebusy.

       The following diagram illustrates how scheduling privileges are
       aggregated according to the above requirements.

       [DAV:all] (aggregate)
           |
           +-- [CALDAV:schedule-deliver] (aggregate)
           |      |
           |      +-- [CALDAV:schedule-deliver-invite]
           |      +-- [CALDAV:schedule-deliver-reply]
           |      +-- [CALDAV:schedule-query-freebusy]
           |
           +-- [CALDAV:schedule-send] (aggregate)
                  |
                  +-- [CALDAV:schedule-send-invite]
                  +-- [CALDAV:schedule-send-reply]
                  +-- [CALDAV:schedule-send-freebusy]

    7.  Additional iCalendar Property Parameters

       This specification defines additional iCalendar property parameters
       to support the CalDAV scheduling extensions.

    7.1.  Schedule Agent Parameter

       Parameter Name:  SCHEDULE-AGENT

       Purpose:  To specify the agent expected to deliver scheduling
          messages to the corresponding "Organizer" or "Attendee".

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       Format Definition:  This property parameter is defined by the
          following notation:

         scheduleagentparam = "SCHEDULE-AGENT" "="
                          ("SERVER"      ; The server handles scheduling
                         / "CLIENT"      ; The client handles scheduling
                         / "NONE"        ; No scheduling
                         / x-name        ; Experimental type
                         / iana-token)   ; Other IANA-registered type
         ;
         ; If the parameter is not present, its value defaults to SERVER.
         ; "x-name" and "iana-token" are defined in Section 3.1 of
         ; [RFC5545].

       Description:  This property parameter MAY be specified on "ORGANIZER"
          or "ATTENDEE" iCalendar properties.  In the absence of this
          parameter, the value "SERVER" MUST be used for the default
          behavior.  The value determines whether or not a scheduling
          operation on a server will cause a scheduling message to be sent
          to the corresponding calendar user identified by the "ORGANIZER"
          or "ATTENDEE" property value.  When the value "SERVER" is
          specified, or the parameter is absent, then it is the server's
          responsibility to send a scheduling message as part of a
          scheduling operation.  When the value "CLIENT" is specified, that
          indicates that the client is handling scheduling messages with the
          calendar user itself.  When "NONE" is specified, no scheduling
          messages are being sent to the calendar user.

          Servers MUST NOT include this parameter in any scheduling messages
          sent as the result of a scheduling operation.

          Clients MUST NOT include this parameter in any scheduling messages
          that they themselves send.

          The parameter value MUST be the same on every "ORGANIZER" property
          in a scheduling object resource.

          The parameter value MUST be the same on each "ATTENDEE" property
          whose values match in a scheduling object resource.

          Servers and clients MUST treat x-name and iana-token values they
          do not recognize the same way as they would the "NONE" value.

       Example:

         ORGANIZER;SCHEDULE-AGENT=SERVER:mailto:bernard@example.com
         ATTENDEE;SCHEDULE-AGENT=NONE:mailto:cyrus@example.com

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    7.2.  Schedule Force Send Parameter

       Parameter Name:  SCHEDULE-FORCE-SEND

       Purpose:  To force a scheduling message to be sent to the calendar
          user specified by the property.

       Format Definition:  This property parameter is defined by the
          following notation:

         scheduleforcesendparam = "SCHEDULE-FORCE-SEND" "="
                                ("REQUEST"    ; Force a "REQUEST"
                               / "REPLY"      ; Force a "REPLY"
                               / iana-token)
         ;
         ; "iana-token" is defined in Section 3.1 of [RFC5545].  Its value
         ; MUST be an IANA-registered iCalendar "METHOD" property value.

       Description:  This property parameter MAY be specified on "ATTENDEE"
          and "ORGANIZER" properties on which the "SCHEDULE-AGENT" property
          parameter is set to the value "SERVER" or is not specified.  This
          property parameter is used to force a server to send a scheduling
          message to a specific calendar user in situations where the server
          would not send a scheduling message otherwise (e.g., when no
          change that warrants the delivery of a new scheduling message was
          performed on the scheduling object resource).  An "Organizer" MAY
          specify this parameter on an "ATTENDEE" property with the value
          "REQUEST" to force a "REQUEST" scheduling message to be sent to
          this "Attendee".  An "Attendee" MAY specify this parameter on the
          "ORGANIZER" with the value "REPLY" to force a "REPLY" scheduling
          message to be sent to the "Organizer".

          Servers MUST NOT preserve this property parameter in scheduling
          object resources, nor include it in any scheduling messages sent
          as the result of a scheduling operation.

          Clients MUST NOT include this parameter in any scheduling messages
          that they themselves send.

          Servers MUST set the "SCHEDULE-STATUS" parameter of the "ATTENDEE"
          or "ORGANIZER" to 2.3 (i.e., "Success; invalid property parameter
          ignored"; see Section 3.6 of [RFC5546]) when the "SCHEDULE-FORCE-
          SEND" parameter is set to an iana-token value they do not
          recognize.

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       Example:

         ORGANIZER;SCHEDULE-FORCE-SEND=REPLY:mailto:cyrus@example.com
         ATTENDEE;SCHEDULE-FORCE-SEND=REQUEST:mailto:bernard@example.com

    7.3.  Schedule Status Parameter

       Parameter Name:  SCHEDULE-STATUS

       Purpose:  To specify the status codes returned from processing of the
          most recent scheduling message sent to the corresponding
          "Attendee", or received from the corresponding "Organizer".

       Format Definition:  This property parameter is defined by the
          following notation:

         schedulestatusparam = "SCHEDULE-STATUS" "="
                             ( statcode
                            / DQUOTE statcode *("," statcode) DQUOTE)
         ;
         ; "statcode" is defined in Section 3.8.8.3 of [RFC5545].  The
         ; value is a single "statcode" or a comma-separated list of
         ; "statcode" values.

       Description:  This property parameter MAY be specified on the
          "ATTENDEE" and "ORGANIZER" properties.

          Servers MUST only add or change this property parameter on any
          "ATTENDEE" properties corresponding to calendar users who were
          sent a scheduling message via a scheduling operation.  Clients
          SHOULD NOT change or remove this parameter if it was provided by
          the server.  In the case where the client is handling the
          scheduling, the client MAY add, change, or remove this parameter
          to indicate the last scheduling message status it received.

          Servers MUST add this parameter to any "ORGANIZER" properties
          corresponding to calendar users who were sent a scheduling message
          reply by an "Attendee" via a scheduling operation.  Clients SHOULD
          NOT change or remove this parameter if it was provided by the
          server.  In the case where the client is handling the scheduling,
          the client MAY add, change, or remove this parameter to indicate
          the last scheduling message status it received.

          Servers MUST NOT include this parameter in any scheduling messages
          sent as the result of a scheduling operation.

          Clients MUST NOT include this parameter in any scheduling messages
          that they themselves send.

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          Values for this property parameter are described in Section 3.2.9.

       Example:

         ATTENDEE;SCHEDULE-STATUS="2.0":mailto:bernard@example.com
         ATTENDEE;SCHEDULE-STATUS="2.0,2.4":mailto:cyrus@example.com

    8.  Additional Message Header Fields

       This specification defines additional HTTP request and response
       headers for use with CalDAV.

    8.1.  Schedule-Reply Request Header

         Schedule-Reply = "Schedule-Reply" ":" ("T" | "F")

       Example:

         Schedule-Reply: F

       When an "Attendee" removes a scheduling object resource as per
       Section 3.2.2.4, and the Schedule-Reply header is set to the value
       "T" (true) or is not present, the server MUST send an appropriate
       reply scheduling message with the "Attendee's" "PARTSTAT" iCalendar
       property parameter value set to "DECLINED" as part of its normal
       scheduling operation processing.

       When the Schedule-Reply header is set to the value "F" (false), the
       server MUST NOT send a scheduling message as part of its normal
       scheduling operation processing.

       The Schedule-Reply request header is used by a client to indicate to
       a server whether or not a scheduling operation ought to occur when an
       "Attendee" deletes a scheduling object resource.  In particular, it
       controls whether a reply scheduling message is sent to the
       "Organizer" as a result of the removal.  There are situations in
       which unsolicited scheduling messages need to be silently removed (or
       ignored) for security or privacy reasons.  This request header allows
       the scheduling object resource to be removed if such a need arises.

    8.2.  Schedule-Tag Response Header

       The Schedule-Tag response header provides the current value of the
       CALDAV:schedule-tag property value.  The behavior of this response
       header is described in Section 3.2.10.

       All scheduling object resources MUST support the Schedule-Tag header.

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         Schedule-Tag = "Schedule-Tag" ":" opaque-tag
         ; "opaque-tag" is defined in Section 3.11 of [RFC2616].

       Example:

         Schedule-Tag: "12ab34-cd56ef"

    8.3.  If-Schedule-Tag-Match Request Header

       The If-Schedule-Tag-Match request header field is used with a method
       to make it conditional.  Clients can set this header to the value
       returned in the Schedule-Tag response header, or the CALDAV:schedule-
       tag property, of a scheduling object resource previously retrieved
       from the server to avoid overwriting "consequential" changes to the
       scheduling object resource.

       All scheduling object resources MUST support the If-Schedule-Tag-
       Match header.

         If-Schedule-Tag-Match = "If-Schedule-Tag-Match" ":" opaque-tag
         ; "opaque-tag" is defined in Section 3.11 of [RFC2616].

       Example:

         If-Schedule-Tag-Match: "12ab34-cd56ef"

    9.  Additional WebDAV Properties

       This specification defines the following new WebDAV properties for
       use with CalDAV.

    9.1.  CALDAV:schedule-calendar-transp Property

       Name:  schedule-calendar-transp

       Namespace:  urn:ietf:params:xml:ns:caldav

       Purpose:  Determines whether the calendar object resources in a
          calendar collection will affect the owner's busy time information.

       Protected:  This property MAY be protected and SHOULD NOT be returned
          by a PROPFIND DAV:allprop request (as defined in Section 14.2 of
          [RFC4918]).

       COPY/MOVE behavior:  This property value SHOULD be kept during a MOVE
          operation, and SHOULD be copied and preserved in a COPY.

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       Description:  This property SHOULD be defined on all calendar
          collections.  If present, it contains one of two XML elements that
          indicate whether the calendar object resources in the calendar
          collection ought to contribute to the owner's busy time.  When the
          CALDAV:opaque element is used, all calendar object resources in
          the corresponding calendar collection MUST contribute to busy
          time, assuming that access privileges and other iCalendar
          properties allow it to.  When the CALDAV:transparent XML element
          is used, the calendar object resources in the corresponding
          calendar collection MUST NOT contribute to busy time.

          If this property is not present on a calendar collection, then the
          default value CALDAV:opaque MUST be assumed.

       Definition:

         <!ELEMENT schedule-calendar-transp (opaque | transparent)>

         <!ELEMENT opaque EMPTY>
         <!-- Affects busy time searches -->

         <!ELEMENT transparent EMPTY>
         <!-- Invisible to busy time searches -->

       Example:

         <C:schedule-calendar-transp
              xmlns:C="urn:ietf:params:xml:ns:caldav">
           <C:opaque/>
         </C:schedule-calendar-transp>

    9.2.  CALDAV:schedule-default-calendar-URL Property

       Name:  schedule-default-calendar-URL

       Namespace:  urn:ietf:params:xml:ns:caldav

       Purpose:  Specifies a default calendar for an "Attendee" where new
          scheduling object resources are created.

       Protected:  This property MAY be protected in the case where a server
          does not support changing the default calendar, or does not
          support a default calendar.

       COPY/MOVE behavior:  This property is only defined on a scheduling
          Inbox collection that cannot be moved or copied.

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       Description:  This property MAY be defined on a scheduling Inbox
          collection.  If present, it contains zero or one DAV:href XML
          elements.  When a DAV:href element is present, its value indicates
          a URL to a calendar collection that is used as the default
          calendar.  When no DAV:href element is present, it indicates that
          there is no default calendar.  In the absence of this property,
          there is no default calendar.  When there is no default calendar,
          the server is free to choose the calendar in which a new
          scheduling object resource is created.  See Section 4.3.

       Definition:

         <!ELEMENT schedule-default-calendar-URL (DAV:href?)>

       Example:

         <C:schedule-default-calendar-URL xmlns:D="DAV:"
             xmlns:C="urn:ietf:params:xml:ns:caldav">
           <D:href>/home/cyrus/calendars/work/</D:href>
         </C:schedule-default-calendar-URL>

    9.3.  CALDAV:schedule-tag Property

       Name:  schedule-tag

       Namespace:  urn:ietf:params:xml:ns:caldav

       Purpose:  Indicates whether a scheduling object resource has had a
          "consequential" change made to it.

       Value:  opaque-tag (defined in Section 3.11 of [RFC2616])

       Protected:  This property MUST be protected, as only the server can
          update the value.

       COPY/MOVE behavior:  This property value is determined by the server
          and MAY be different from the value on the source resource.

       Description:  The CALDAV:schedule-tag property MUST be defined on all
          scheduling object resources.  This property is described in
          Section 3.2.10.

       Definition:

         <!ELEMENT schedule-tag (#PCDATA)>

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       Example:

         <C:schedule-tag xmlns:C="urn:ietf:params:xml:ns:caldav"
         >"12345-67890"</C:schedule-tag>

    10.  XML Element Definitions

    10.1.  CALDAV:schedule-response XML Element

       Name:  schedule-response

       Namespace:  urn:ietf:params:xml:ns:caldav

       Purpose:  Contains the set of responses for a POST method request.

       Description:  See Section 5.

       Definition:

         <!ELEMENT schedule-response (response*)>

    10.2.  CALDAV:response XML Element

       Name:  response

       Namespace:  urn:ietf:params:xml:ns:caldav

       Purpose:  Contains a single response for a POST method request.

       Description:  See Section 5.

       Definition:

         <!ELEMENT response (recipient,
                             request-status,
                             calendar-data?,
                             DAV:error?,
                             DAV:responsedescription?)>

         <!-- CALDAV:calendar-data is defined in Section 9.6 of
         RFC 4791 and when used here uses the definition with
         content (#PCDATA) only. -->

    10.3.  CALDAV:recipient XML Element

       Name:  recipient

       Namespace:  urn:ietf:params:xml:ns:caldav

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       Purpose:  The calendar user address that the enclosing response for a
          POST method request is for.

       Description:  See Section 5.

       Definition:

         <!ELEMENT recipient (DAV:href)>

    10.4.  CALDAV:request-status XML Element

       Name:  request-status

       Namespace:  urn:ietf:params:xml:ns:caldav

       Purpose:  The iTIP "REQUEST-STATUS" property value for this response.

       Description:  See Section 5.

       Definition:

         <!ELEMENT request-status (#PCDATA)>

    11.  Security Considerations

       The process of scheduling involves the sending and receiving of
       scheduling messages.  As a result, the security problems related to
       messaging in general are relevant here.  In particular, the
       authenticity of the scheduling messages needs to be verified.
       Servers and clients MUST use an HTTP connection protected with
       Transport Layer Security (TLS) as defined in [RFC2818] for all
       scheduling operations.  Clients MUST use the procedures detailed in
       Section 6 of [RFC6125] to verify the authenticity of the server.
       Servers MUST make use of HTTP authentication [RFC2617] to verify the
       authenticity of the calendar user for whom the client is sending
       requests.

    11.1.  Preventing Denial-of-Service Attacks

       Servers MUST ensure that clients cannot consume excessive server
       resources by carrying out "large" scheduling operations.  In
       particular, servers SHOULD enforce CALDAV:max-resource-size, CALDAV:
       max-instances, and CALDAV:max-attendees-per-instance preconditions as
       applicable for scheduling Inbox and Outbox collections.

    Daboo & Desruisseaux         Standards Track                   [Page 51]

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    11.2.  Verifying Scheduling Operations

       When handling a scheduling operation:

       1.  Servers MUST verify that the principal associated with the DAV:
           owner of the calendar collection in which a scheduling object
           resource is being manipulated contains a CALDAV:schedule-outbox-
           URL property value.

       2.  Servers MUST verify that the currently authenticated user has the
           CALDAV:schedule-send privilege, or a sub-privilege aggregated
           under this privilege, on the scheduling Outbox collection of the
           DAV:owner of the calendar collection in which a scheduling object
           resource is being manipulated.

       3.  Servers MUST only deliver scheduling messages to recipients when
           the CALDAV:schedule-deliver privilege, or a sub-privilege
           aggregated under this privilege, is granted on the recipient's
           scheduling Inbox collection for the principal associated with the
           DAV:owner of the calendar collection in which a scheduling object
           resource is being manipulated.

       4.  To prevent impersonation of calendar users, the server MUST
           verify that the "ORGANIZER" property in an organizer scheduling
           object resource matches one of the calendar user addresses of the
           DAV:owner of the calendar collection in which the resource is
           stored.

       5.  To prevent spoofing of an existing scheduling object resource,
           servers MUST verify that the "UID" iCalendar property value in a
           new scheduling object resource does not match that of an existing
           scheduling object resource with a different "ORGANIZER" property
           value.

    11.3.  Verifying Busy Time Information Requests

       When handling a POST request on a scheduling Outbox collection:

       1.  Servers MUST verify that the principal associated with the
           calendar user address specified in the "ORGANIZER" property of
           the scheduling message data in the request contains a CALDAV:
           schedule-outbox-URL property value that matches the scheduling
           Outbox collection targeted by the request.

       2.  Servers MUST verify that the currently authenticated user has the
           CALDAV:schedule-send privilege, or a sub-privilege aggregated
           under this privilege, on the scheduling Outbox collection
           targeted by the request.

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       3.  Servers MUST only return valid freebusy information for
           recipients when the CALDAV:schedule-deliver privilege, or a
           sub-privilege aggregated under this privilege, is granted on the
           recipient's scheduling Inbox collection for the principal
           associated with the DAV:owner of the scheduling Outbox collection
           targeted by the request.

    11.4.  Privacy Issues

       This specification only defines how calendar users on the same server
       are able to schedule with each other -- unauthenticated users have no
       way to carry out scheduling operations.  Access control privileges
       (as per Section 6) can control which of those users can schedule with
       others.  Calendar users not wishing to expose their calendar
       information to other users can do so by denying privileges to
       specific users, or all users, for all scheduling operations, or
       perhaps only freebusy.

       "Attendees" can also use the Schedule-Reply request header
       (Section 8.1) with the value set to "F" to prevent notification to an
       "Organizer" that a scheduling object resource was deleted.  This
       allows "Attendees" to remove unwanted scheduling messages without any
       response to the "Organizer".

       Servers MUST NOT expose any private iCalendar data, or WebDAV
       resource state information (URLs, WebDAV properties, etc.) for one
       calendar user to another via scheduling messages or error responses
       to scheduling operations.  In particular, as per Section 8.1 of
       [RFC4918], authorization errors MUST take preference over other
       errors.

    11.5.  Mitigation of iTIP Threats

       Section 6.1 of iTIP [RFC5546] defines a set of potential threats in a
       scheduling system, and Section 6.2 of [RFC5546] defines
       recommendations on how those can be addressed in protocols using
       iTIP.  This specification addresses the iTIP threats in the following
       manner:

       Spoofing the "Organizer":  Addressed by item 4 in Section 11.2.

       Spoofing the "Attendee":  Addressed by Section 3.2.2.1 and item 2 in
          Section 11.2.

       Unauthorized Replacement of the "Organizer":  Addressed by item 5 in
          Section 11.2.

       Eavesdropping and Data Integrity:  Addressed by requiring TLS.

    Daboo & Desruisseaux         Standards Track                   [Page 53]

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       Flooding a Calendar:  Addressed by requirements in Section 11.1.

       Unauthorized REFRESH Requests:  This specification does not support
          the REFRESH method.

    12.  IANA Considerations

    12.1.  Message Header Field Registrations

       The message header fields below have been added to the Permanent
       Message Header Field Registry (see [RFC3864]).

    12.1.1.  Schedule-Reply

       Header field name: Schedule-Reply

       Applicable protocol: http

       Status: standard

       Author/Change controller: IETF

       Specification document(s): this specification (Section 8.1)

       Related information: none

    12.1.2.  Schedule-Tag

       Header field name: Schedule-Tag

       Applicable protocol: http

       Status: standard

       Author/Change controller: IETF

       Specification document(s): this specification (Section 8.2)

       Related information: none

    12.1.3.  If-Schedule-Tag-Match

       Header field name: If-Schedule-Tag-Match

       Applicable protocol: http

       Status: standard

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    RFC 6638                    CalDAV Scheduling                  June 2012

       Author/Change controller: IETF

       Specification document(s): this specification (Section 8.3)

       Related information: none

    12.2.  iCalendar Property Parameter Registrations

       The following iCalendar property parameter names have been added to
       the iCalendar Parameters Registry defined in Section 8.3.3 of
       [RFC5545].

             +---------------------+---------+-----------------------+
             | Parameter           | Status  | Reference             |
             +---------------------+---------+-----------------------+
             | SCHEDULE-AGENT      | Current | RFC 6638, Section 7.1 |
             |                     |         |                       |
             | SCHEDULE-STATUS     | Current | RFC 6638, Section 7.3 |
             |                     |         |                       |
             | SCHEDULE-FORCE-SEND | Current | RFC 6638, Section 7.2 |
             +---------------------+---------+-----------------------+

    12.3.  iCalendar REQUEST-STATUS Value Registrations

       The following iCalendar "REQUEST-STATUS" values have been added to
       the iCalendar REQUEST-STATUS Value Registry defined in Section 7.3 of
       [RFC5546].

               +-------------+---------+---------------------------+
               | Status Code | Status  | Reference                 |
               +-------------+---------+---------------------------+
               | 1.0         | Current | RFC 6638, Section 3.2.9.1 |
               |             |         |                           |
               | 1.1         | Current | RFC 6638, Section 3.2.9.2 |
               |             |         |                           |
               | 1.2         | Current | RFC 6638, Section 3.2.9.3 |
               +-------------+---------+---------------------------+

    12.4.  Additional iCalendar Elements Registries

       Per this specification, two new IANA registries for iCalendar
       elements have been added.  Additional codes MAY be used, provided the
       process described in Section 8.2.1 of [RFC5545] is used to register
       them.

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    12.4.1.  Schedule Agent Values Registry

       The following table has been used to initialize the Schedule Agent
       Values Registry.

               +----------------+---------+-----------------------+
               | Schedule Agent | Status  | Reference             |
               +----------------+---------+-----------------------+
               | SERVER         | Current | RFC 6638, Section 7.1 |
               |                |         |                       |
               | CLIENT         | Current | RFC 6638, Section 7.1 |
               |                |         |                       |
               | NONE           | Current | RFC 6638, Section 7.1 |
               +----------------+---------+-----------------------+

    12.4.2.  Schedule Force Send Values Registry

       The following table has been used to initialize the Schedule Force
       Send Values Registry.

             +---------------------+---------+-----------------------+
             | Schedule Force Send | Status  | Reference             |
             +---------------------+---------+-----------------------+
             | REQUEST             | Current | RFC 6638, Section 7.2 |
             |                     |         |                       |
             | REPLY               | Current | RFC 6638, Section 7.2 |
             +---------------------+---------+-----------------------+

    13.  Acknowledgements

       The authors would like to thank the following individuals for
       contributing their ideas and support for writing this specification:
       Mike Douglass, Lisa Dusseault, Red Dutta, Jacob Farkas, Jeffrey
       Harris, Helge Hess, Eliot Lear, Andrew McMillan, Alexey Melnikov,
       Arnaud Quillaud, Julian F. Reschke, Wilfredo Sanchez Vega, and Simon
       Vaillancourt.

       The authors would also like to thank the Calendaring and Scheduling
       Consortium for advice with this specification, and for organizing
       interoperability testing events to help refine it.

    Daboo & Desruisseaux         Standards Track                   [Page 56]

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    14.  References

    14.1.  Normative References

       [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.

       [RFC2616]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
                  Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
                  Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.

       [RFC2617]  Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
                  Leach, P., Luotonen, A., and L. Stewart, "HTTP
                  Authentication: Basic and Digest Access Authentication",
                  RFC 2617, June 1999.

       [RFC2818]  Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000.

       [RFC3744]  Clemm, G., Reschke, J., Sedlar, E., and J. Whitehead, "Web
                  Distributed Authoring and Versioning (WebDAV)
                  Access Control Protocol", RFC 3744, May 2004.

       [RFC3864]  Klyne, G., Nottingham, M., and J. Mogul, "Registration
                  Procedures for Message Header Fields", BCP 90, RFC 3864,
                  September 2004.

       [RFC4791]  Daboo, C., Desruisseaux, B., and L. Dusseault,
                  "Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
                  March 2007.

       [RFC4918]  Dusseault, L., Ed., "HTTP Extensions for Web Distributed
                  Authoring and Versioning (WebDAV)", RFC 4918, June 2007.

       [RFC5234]  Crocker, D., Ed., and P. Overell, "Augmented BNF for
                  Syntax Specifications: ABNF", STD 68, RFC 5234,
                  January 2008.

       [RFC5545]  Desruisseaux, B., Ed., "Internet Calendaring and
                  Scheduling Core Object Specification (iCalendar)",
                  RFC 5545, September 2009.

       [RFC5546]  Daboo, C., Ed., "iCalendar Transport-Independent
                  Interoperability Protocol (iTIP)", RFC 5546,
                  December 2009.

    Daboo & Desruisseaux         Standards Track                   [Page 57]

    RFC 6638                    CalDAV Scheduling                  June 2012

       [RFC6125]  Saint-Andre, P. and J. Hodges, "Representation and
                  Verification of Domain-Based Application Service Identity
                  within Internet Public Key Infrastructure Using X.509
                  (PKIX) Certificates in the Context of Transport Layer
                  Security (TLS)", RFC 6125, March 2011.

       [W3C.REC-xml-20081126]
                  Bray, T., Paoli, J., Sperberg-McQueen, C., Maler, E.,
                  and F. Yergeau, "Extensible Markup Language (XML) 1.0
                  (Fifth Edition)", World Wide Web Consortium
                  Recommendation REC-xml-20081126, November 2008,
                  <http://www.w3.org/TR/2008/REC-xml-20081126>.

    14.2.  Informative References

       [RFC6047]  Melnikov, A., Ed., "iCalendar Message-Based
                  Interoperability Protocol (iMIP)", RFC 6047,
                  December 2010.

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    RFC 6638                    CalDAV Scheduling                  June 2012

    Appendix A.  Scheduling Privileges Summary

    A.1.  Scheduling Inbox Privileges

       The following tables specify which scheduling privileges grant the
       right to a calendar user to deliver a scheduling message to the
       scheduling Inbox collection of another calendar user.  The
       appropriate behavior depends on the calendar component type as well
       as the scheduling "METHOD" specified in the scheduling message.

                                     +--------------------------------+
                                     |  METHOD for VEVENT and VTODO   |
       +-----------------------------+---------+-------+-----+--------+
       | Scheduling Inbox Privilege  | REQUEST | REPLY | ADD | CANCEL |
       +-----------------------------+---------+-------+-----+--------+
       | schedule-deliver            |    *    |   *   |  *  |   *    |
       |   schedule-deliver-invite   |    *    |       |  *  |   *    |
       |   schedule-deliver-reply    |         |   *   |     |        |
       |   schedule-query-freebusy   |         |       |     |        |
       +-----------------------------+---------+-------+-----+--------+

                                     +----------------------+
                                     | METHOD for VFREEBUSY |
       +-----------------------------+----------------------+
       | Scheduling Inbox Privilege  |       REQUEST        |
       +-----------------------------+----------------------+
       | schedule-deliver            |          *           |
       |   schedule-deliver-invite   |                      |
       |   schedule-deliver-reply    |                      |
       |   schedule-query-freebusy   |          *           |
       +-----------------------------+----------------------+

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    RFC 6638                    CalDAV Scheduling                  June 2012

    A.2.  Scheduling Outbox Privileges

       The following tables specify which scheduling privileges grant the
       right to a calendar user to perform busy time information requests
       and to submit scheduling messages to other calendar users as the
       result of a scheduling operation.  The appropriate behavior depends
       on the calendar component type as well as the scheduling "METHOD"
       specified in the scheduling message.

                                     +--------------------------------+
                                     |  METHOD for VEVENT and VTODO   |
       +-----------------------------+---------+-------+-----+--------+
       | Scheduling Outbox Privilege | REQUEST | REPLY | ADD | CANCEL |
       +-----------------------------+---------+-------+-----+--------+
       | schedule-send               |    *    |   *   |  *  |   *    |
       |   schedule-send-invite      |    *    |       |  *  |   *    |
       |   schedule-send-reply       |         |   *   |     |        |
       |   schedule-send-freebusy    |         |       |     |        |
       +-----------------------------+---------+-------+-----+--------+

                                     +----------------------+
                                     | METHOD for VFREEBUSY |
       +-----------------------------+----------------------+
       | Scheduling Outbox Privilege |       REQUEST        |
       +-----------------------------+----------------------+
       | schedule-send               |          *           |
       |   schedule-send-invite      |                      |
       |   schedule-send-reply       |                      |
       |   schedule-send-freebusy    |          *           |
       +-----------------------------+----------------------+

    Appendix B.  Example Scheduling Operations

       This section describes some example scheduling operations that give a
       general idea of how scheduling is carried out between CalDAV clients
       and servers from the perspective of meeting "Organizers" and
       "Attendees".

       The server is assumed to be hosted in the "example.com" domain, and
       users whose email addresses are at the "example.com" domain are
       assumed to be hosted by the server.  In addition, the email addresses
       in the "example.net" domain are also valid email addresses for
       calendar users hosted by the server.  Calendar users with an email
       address at the "example.org" domain are assumed to not be hosted by
       the server.

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       In the following examples, the requests and responses are incomplete
       and are only for illustrative purposes.  In particular, HTTP
       authentication headers and behaviors are not shown, even though they
       are required in normal operation.

    B.1.  Example: "Organizer" Inviting Multiple "Attendees"

       In the following example, Cyrus invites Wilfredo, Bernard, and Mike
       to a single instance event by simply creating a new scheduling object
       resource in one of his calendar collections by using the PUT method.

       >> Request <<

       PUT /home/cyrus/calendars/work/9263504FD3AD.ics HTTP/1.1
       Host: cal.example.com
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx
       If-None-Match: *

       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Client//EN
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090602T185254Z
       DTSTART:20090602T160000Z
       DTEND:20090602T170000Z
       TRANSP:OPAQUE
       SUMMARY:Lunch
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
        mailto:cyrus@example.com
       ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
        =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:wilfredo@
        example.com
       ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
        NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@ex
        ample.net
       ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
        CTION;RSVP=TRUE:mailto:mike@example.org
       END:VEVENT
       END:VCALENDAR

       >> Response <<

       HTTP/1.1 201 Created
       Content-Length: 0

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    RFC 6638                    CalDAV Scheduling                  June 2012

       Date: Tue, 02 Jun 2009 18:52:54 GMT
       Last-Modified: Tue, 02 Jun 2009 18:52:54 GMT
       ETag: "d85561cfe74a4e785eb4639451b434fb"
       Schedule-Tag: "488177c8-2ea7-4176-a6cb-fab8cfccdea2"

       Once the event creation has been completed, Cyrus's client will
       retrieve the event back from the server to get the schedule status of
       each "Attendee", as well as record the Schedule-Tag value for future
       use.  In this example, the server reports that a scheduling message
       was delivered to Wilfredo, a scheduling message is still pending for
       Bernard, and the server was unable to deliver a scheduling message to
       Mike.

       >> Request <<

       GET /home/cyrus/calendars/work/9263504FD3AD.ics HTTP/1.1
       Host: cal.example.com

       >> Response <<

       HTTP/1.1 200 OK
       Date: Tue, 02 Jun 2009 18:52:58 GMT
       Last-Modified: Tue, 02 Jun 2009 18:52:58 GMT
       ETag: "eb897deabc8939589da116714bc99265"
       Schedule-Tag: "488177c8-2ea7-4176-a6cb-fab8cfccdea2"
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx

       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Server//EN
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090602T185300Z
       DTSTART:20090602T160000Z
       DTEND:20090602T170000Z
       TRANSP:OPAQUE
       SUMMARY:Lunch
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
        mailto:cyrus@example.com
       ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
        =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=
        1.2:mailto:wilfredo@e
        xample.com

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       ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
        NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=
        1.0:mailto:bernard@example.net
       ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
        CTION;RSVP=TRUE;SCHEDULE-STATUS=3.7:mailto:mike@example.org
       END:VEVENT
       END:VCALENDAR

    B.2.  Example: "Attendee" Receiving an Invitation

       In the following example, Wilfredo's client retrieves and deletes the
       new scheduling message that appeared in his scheduling Inbox
       collection after the server automatically processed it and created a
       new scheduling object resource in his default calendar collection.

       >> Request <<

       GET /home/wilfredo/calendars/inbox/27d93fc0a58c.ics HTTP/1.1
       Host: cal.example.com

       >> Response <<

       HTTP/1.1 200 OK
       Date: Tue, 02 Jun 2009 18:59:58 GMT
       Last-Modified: Tue, 02 Jun 2009 18:59:58 GMT
       ETag: "da116714bc9926c89395895eb897deab"
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx

       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Server//EN
       METHOD:REQUEST
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090602T185254Z
       DTSTART:20090602T160000Z
       DTEND:20090602T170000Z
       TRANSP:OPAQUE
       SUMMARY:Lunch
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
        mailto:cyrus@example.com
       ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
        =NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:wilfredo@
        example.com

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       ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
        NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@ex
        ample.net
       ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
        CTION;RSVP=TRUE:mailto:mike@example.org
       END:VEVENT
       END:VCALENDAR

       >> Request <<

       DELETE /home/wilfredo/calendars/inbox/27d93fc0a58c.ics HTTP/1.1
       Host: cal.example.com

       >> Response <<

       HTTP/1.1 204 No Content
       Date: Tue, 02 Jun 2009 20:40:36 GMT

    B.3.  Example: "Attendee" Replying to an Invitation

       In the following example, Wilfredo accepts Cyrus's invitation and
       sets an alarm reminder on the event.  It uses the If-Schedule-Tag-
       Match precondition behavior to ensure it does not overwrite any
       significant changes from the "Organizer" that might have occurred
       after it retrieved the initial resource data.

       >> Request <<

       PUT /home/wilfredo/calendars/work/BB64861C2228.ics HTTP/1.1
       Host: cal.example.com
       If-Schedule-Tag-Match: "e78f23ed-0188-4bab-938d-2aeb3324c7e8"
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx

       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Client//EN
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090602T185254Z
       DTSTART:20090602T160000Z
       DTEND:20090602T170000Z
       TRANSP:OPAQUE
       SUMMARY:Lunch
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
        mailto:cyrus@example.com

    Daboo & Desruisseaux         Standards Track                   [Page 64]

    RFC 6638                    CalDAV Scheduling                  June 2012

       ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
        =ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:wilfredo@exam
        ple.com
       ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
        NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@ex
        ample.net
       ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
        CTION;RSVP=TRUE:mailto:mike@example.org
       BEGIN:VALARM
       TRIGGER:-PT15M
       ACTION:DISPLAY
       DESCRIPTION:Reminder
       END:VALARM
       END:VEVENT
       END:VCALENDAR

       >> Response <<

       HTTP/1.1 200 OK
       Content-Length: 0
       Date: Tue, 02 Jun 2009 18:57:54 GMT
       Last-Modified: Tue, 02 Jun 2009 18:57:54 GMT
       ETag: "eb4639451b434fbd85561cfe74a4e785"
       Schedule-Tag: "8893ee45-eb9d-428f-b53c-c777daf19e41"

       Once the event modification has been completed, Wilfredo's client
       will retrieve the event back from the server to get the schedule
       status of the "Organizer".

       >> Request <<

       GET /home/wilfredo/calendars/work/BB64861C2228.ics HTTP/1.1
       Host: cal.example.com

       >> Response <<

       HTTP/1.1 200 OK
       Date: Tue, 02 Jun 2009 19:03:03 GMT
       Last-Modified: Tue, 02 Jun 2009 19:02:21 GMT
       ETag: "5eb897deabda116714bc9926c8939589"
       Schedule-Tag: "8893ee45-eb9d-428f-b53c-c777daf19e41"
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx

    Daboo & Desruisseaux         Standards Track                   [Page 65]

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       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Client//EN
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090602T190221Z
       DTSTART:20090602T160000Z
       DTEND:20090602T170000Z
       TRANSP:OPAQUE
       SUMMARY:Lunch
       ORGANIZER;CN="Cyrus Daboo";SCHEDULE-STATUS=1.2:mailto:cyrus@ex
        ample.com
       ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
        mailto:cyrus@example.com
       ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
        =ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:wilfredo@exam
        ple.com
       ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
        NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@ex
        ample.net
       ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
        CTION;RSVP=TRUE:mailto:mike@example.org
       BEGIN:VALARM
       TRIGGER:-PT15M
       ACTION:DISPLAY
       DESCRIPTION:Reminder
       END:VALARM
       END:VEVENT
       END:VCALENDAR

    B.4.  Example: "Organizer" Receiving a Reply to an Invitation

       On reception of Wilfredo's reply, Cyrus's server will automatically
       update Cyrus's scheduling object resource, make Wilfredo's scheduling
       message available in Cyrus's scheduling Inbox collection, and deliver
       an updated scheduling message to Bernard to share Wilfredo's updated
       participation status.  In this example, Cyrus's client retrieves and
       deletes this scheduling message in his scheduling Inbox collection.

       >> Request <<

       GET /home/cyrus/calendars/inbox/c0a58c27d93f.ics HTTP/1.1
       Host: cal.example.com

    Daboo & Desruisseaux         Standards Track                   [Page 66]

    RFC 6638                    CalDAV Scheduling                  June 2012

       >> Response <<

       HTTP/1.1 200 OK
       Date: Tue, 02 Jun 2009 19:05:02 GMT
       Last-Modified: Tue, 02 Jun 2009 19:04:20 GMT
       ETag: "9265eb897deabc8939589da116714bc9"
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx

       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Server//EN
       METHOD:REPLY
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090602T185754Z
       DTSTART:20090602T160000Z
       DTEND:20090602T170000Z
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Wilfredo Sanchez Vega";PARTSTAT=ACCEPTED:mailto:w
        ilfredo@example.com
       REQUEST-STATUS:2.0;Success
       END:VEVENT
       END:VCALENDAR

       >> Request <<

       DELETE /home/cyrus/calendars/inbox/c0a58c27d93f.ics HTTP/1.1
       Host: cal.example.com

       >> Response <<

       HTTP/1.1 204 No Content
       Date: Tue, 02 Jun 2009 19:05:05 GMT

       Cyrus's client then retrieves the event back from the server with
       Wilfredo's updated participation status.

       >> Request <<

       GET /home/cyrus/calendars/work/9263504FD3AD.ics HTTP/1.1
       Host: cal.example.com

    Daboo & Desruisseaux         Standards Track                   [Page 67]

    RFC 6638                    CalDAV Scheduling                  June 2012

       >> Response <<

       HTTP/1.1 200 OK
       Date: Tue, 02 Jun 2009 19:05:02 GMT
       Last-Modified: Tue, 02 Jun 2009 19:04:20 GMT
       ETag: "eb897deabc8939589da116714bc99265"
       Schedule-Tag: "132cab27-1fe3-67ab-de13-abd348d1dee3"
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx

       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Server//EN
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090602T190420Z
       DTSTART:20090602T160000Z
       DTEND:20090602T170000Z
       TRANSP:OPAQUE
       SUMMARY:Lunch
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
        mailto:cyrus@example.com
       ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT
        =ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=2.0:
        mailto:wilfredo@example.com
       ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
        NEEDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE;SCHEDULE-STATUS=1
        .0:mailto:bernard@example.net
       ATTENDEE;CN="Mike Douglass";CUTYPE=INDIVIDUAL;PARTSTAT=NEEDS-A
        CTION;RSVP=TRUE;SCHEDULE-STATUS=3.7:mailto:mike@example.org
       END:VEVENT
       END:VCALENDAR

    Daboo & Desruisseaux         Standards Track                   [Page 68]

    RFC 6638                    CalDAV Scheduling                  June 2012

    B.5.  Example: "Organizer" Requesting Busy Time Information

       In this example, Cyrus requests the busy time information of
       Wilfredo, Bernard, and Mike.

       >> Request <<

       POST /home/cyrus/calendars/outbox/ HTTP/1.1
       Host: cal.example.com
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx

       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Client//EN
       METHOD:REQUEST
       BEGIN:VFREEBUSY
       UID:4FD3AD926350
       DTSTAMP:20090602T190420Z
       DTSTART:20090602T000000Z
       DTEND:20090604T000000Z
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Wilfredo Sanchez Vega":mailto:wilfredo@example.com
       ATTENDEE;CN="Bernard Desruisseaux":mailto:bernard@example.net
       ATTENDEE;CN="Mike Douglass":mailto:mike@example.org
       END:VFREEBUSY
       END:VCALENDAR

       >> Response <<

       HTTP/1.1 200 OK
       Date: Tue, 02 Jun 2009 20:07:34 GMT
       Content-Type: application/xml; charset="utf-8"
       Content-Length: xxxx

       <?xml version="1.0" encoding="utf-8" ?>
       <C:schedule-response xmlns:D="DAV:"
              xmlns:C="urn:ietf:params:xml:ns:caldav">
       <C:response>
       <C:recipient>
       <D:href>mailto:wilfredo@example.com</D:href>
       </C:recipient>
       <C:request-status>2.0;Success</C:request-status>
       <C:calendar-data>BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Server//EN
       METHOD:REPLY
       BEGIN:VFREEBUSY

    Daboo & Desruisseaux         Standards Track                   [Page 69]

    RFC 6638                    CalDAV Scheduling                  June 2012

       UID:4FD3AD926350
       DTSTAMP:20090602T200733Z
       DTSTART:20090602T000000Z
       DTEND:20090604T000000Z
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Wilfredo Sanchez Vega":mailto:wilfredo@example.com
       FREEBUSY;FBTYPE=BUSY:20090602T110000Z/20090602T120000Z
       FREEBUSY;FBTYPE=BUSY:20090603T170000Z/20090603T180000Z
       END:VFREEBUSY
       END:VCALENDAR
       </C:calendar-data>
       </C:response>
       <C:response>
       <C:recipient>
       <D:href>mailto:bernard@example.net</D:href>
       </C:recipient>
       <C:request-status>2.0;Success</C:request-status>
       <C:calendar-data>BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Server//EN
       METHOD:REPLY
       BEGIN:VFREEBUSY
       UID:4FD3AD926350
       DTSTAMP:20090602T200733Z
       DTSTART:20090602T000000Z
       DTEND:20090604T000000Z
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Bernard Desruisseaux":mailto:bernard@example.net
       FREEBUSY;FBTYPE=BUSY:20090602T150000Z/20090602T160000Z
       FREEBUSY;FBTYPE=BUSY:20090603T090000Z/20090603T100000Z
       FREEBUSY;FBTYPE=BUSY:20090603T180000Z/20090603T190000Z
       END:VFREEBUSY
       END:VCALENDAR
       </C:calendar-data>
       </C:response>
       <C:response>
       <C:recipient>
       <D:href>mailto:mike@example.org</D:href>
       </C:recipient>
       <C:request-status>3.7;Invalid calendar user</C:request-status>
       </C:response>
       </C:schedule-response>

    Daboo & Desruisseaux         Standards Track                   [Page 70]

    RFC 6638                    CalDAV Scheduling                  June 2012

    B.6.  Example: User Attempting to Invite "Attendee" on Behalf of
          "Organizer"

       In the following example, Cyrus attempts to create, on behalf of
       Wilfredo, an event with Bernard specified as an "Attendee".  The
       request fails, since Wilfredo didn't grant Cyrus the right to invite
       other calendar users on his behalf.

       >> Request <<

       PUT /home/wilfredo/calendars/work/def456.ics HTTP/1.1
       Host: cal.example.com
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx
       If-None-Match: *

       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Client//EN
       BEGIN:VEVENT
       UID:3504F926D3AD
       SEQUENCE:0
       DTSTAMP:20090602T190221Z
       DTSTART:20090602T230000Z
       DTEND:20090603T000000Z
       TRANSP:OPAQUE
       SUMMARY:Dinner
       ORGANIZER;CN="Wilfredo Sanchez Vega":mailto:wilfredo@example.com
       ATTENDEE;CN="Wilfredo Sanchez Vega";CUTYPE=INDIVIDUAL;PARTSTAT=A
        CCEPTED:mailto:wilfredo@example.com
       ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=NE
        EDS-ACTION;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
        e.net
       END:VEVENT
       END:VCALENDAR

    Daboo & Desruisseaux         Standards Track                   [Page 71]

    RFC 6638                    CalDAV Scheduling                  June 2012

       >> Response <<

       HTTP/1.1 403 Forbidden
       Content-Type: application/xml; charset="utf-8"
       Content-Length: xxxx

       <?xml version="1.0" encoding="utf-8" ?>
       <D:error xmlns:D="DAV:" xmlns:C="urn:ietf:params:xml:ns:caldav">
         <D:need-privileges>
           <D:resource>
             <D:href>/home/wilfredo/calendars/outbox/</D:href>
             <D:privilege><C:schedule-send-invite/></D:privilege>
           </D:resource>
         </D:need-privileges>
       </D:error>

    B.7.  Example: "Attendee" Declining an Instance of a Recurring Event

       In the following example, Bernard declines the second recurrence
       instance of a daily recurring event he's been invited to by Cyrus.

       >> Request <<

       PUT /home/bernard/calendars/work/4FD3AD926350.ics HTTP/1.1
       Host: cal.example.com
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx
       If-Schedule-Tag-Match: "7775FB30-7534-489E-A79A-0EA147B933EB"

       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Client//EN
       BEGIN:VTIMEZONE
       TZID:America/Montreal
       BEGIN:STANDARD
       DTSTART:20071104T020000
       RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
       TZNAME:EST
       TZOFFSETFROM:-0400
       TZOFFSETTO:-0500
       END:STANDARD
       BEGIN:DAYLIGHT
       DTSTART:20070311T020000
       RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
       TZNAME:EDT
       TZOFFSETFROM:-0500
       TZOFFSETTO:-0400
       END:DAYLIGHT

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       END:VTIMEZONE
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090602T185254Z
       DTSTART;TZID=America/Montreal:20090601T150000
       DTEND;TZID=America/Montreal:20090601T160000
       RRULE:FREQ=DAILY;INTERVAL=1;COUNT=5
       TRANSP:OPAQUE
       SUMMARY:Review Internet-Draft
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
        mailto:cyrus@example.com
       ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
        ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
        e.net
       END:VEVENT
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090603T183823Z
       RECURRENCE-ID;TZID=America/Montreal:20090602T150000
       DTSTART;TZID=America/Montreal:20090602T150000
       DTEND;TZID=America/Montreal:20090602T160000
       TRANSP:TRANSPARENT
       SUMMARY:Review Internet-Draft
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
        mailto:cyrus@example.com
       ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
        DECLINED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
        e.net
       END:VEVENT
       END:VCALENDAR

       >> Response <<

       HTTP/1.1 200 OK
       Content-Length: 0
       Date: Tue, 02 Jun 2009 18:52:54 GMT
       Last-Modified: Tue, 02 Jun 2009 18:52:54 GMT
       ETag: "d85561cfe74a4e785eb4639451b434fb"
       Schedule-Tag: "488177c8-2ea7-4176-a6cb-fab8cfccdea2"

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    RFC 6638                    CalDAV Scheduling                  June 2012

       Bernard's participation status update will cause his server to
       deliver a scheduling message to Cyrus.  Cyrus's client will find the
       following reply message from Bernard in Cyrus's scheduling Inbox
       collection:

       >> Request <<

       GET /home/cyrus/calendars/inbox/9263504FD3AD.ics HTTP/1.1
       Host: cal.example.com

       >> Response <<

       HTTP/1.1 200 OK
       Date: Tue, 02 Jun 2009 18:52:58 GMT
       Last-Modified: Tue, 02 Jun 2009 18:52:58 GMT
       ETag: "eb897deabc8939589da116714bc99265"
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx

       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Client//EN
       METHOD:REPLY
       BEGIN:VTIMEZONE
       TZID:America/Montreal
       BEGIN:STANDARD
       DTSTART:20071104T020000
       RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
       TZNAME:EST
       TZOFFSETFROM:-0400
       TZOFFSETTO:-0500
       END:STANDARD
       BEGIN:DAYLIGHT
       DTSTART:20070311T020000
       RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
       TZNAME:EDT
       TZOFFSETFROM:-0500
       TZOFFSETTO:-0400
       END:DAYLIGHT
       END:VTIMEZONE
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090603T183823Z
       RECURRENCE-ID;TZID=America/Montreal:20090602T150000
       DTSTART;TZID=America/Montreal:20090602T150000
       DTEND;TZID=America/Montreal:20090602T160000
       SUMMARY:Review Internet-Draft

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    RFC 6638                    CalDAV Scheduling                  June 2012

       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Bernard Desruisseaux";PARTSTAT=DECLINED:
        mailto:bernard@example.net
       REQUEST-STATUS:2.0;Success
       END:VEVENT
       END:VCALENDAR

    B.8.  Example: "Attendee" Removing an Instance of a Recurring Event

       In the following example, Bernard removes from his calendar the third
       recurrence instance of a daily recurring event he's been invited to
       by Cyrus.  This is accomplished by the addition of an "EXDATE"
       property to the scheduling object resource stored by Bernard.

       >> Request <<

       PUT /home/bernard/calendars/work/4FD3AD926350.ics HTTP/1.1
       Host: cal.example.com
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx
       If-Schedule-Tag-Match: "488177c8-2ea7-4176-a6cb-fab8cfccdea2"

       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Client//EN
       BEGIN:VTIMEZONE
       TZID:America/Montreal
       BEGIN:STANDARD
       DTSTART:20071104T020000
       RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
       TZNAME:EST
       TZOFFSETFROM:-0400
       TZOFFSETTO:-0500
       END:STANDARD
       BEGIN:DAYLIGHT
       DTSTART:20070311T020000
       RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
       TZNAME:EDT
       TZOFFSETFROM:-0500
       TZOFFSETTO:-0400
       END:DAYLIGHT
       END:VTIMEZONE
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090602T185254Z
       DTSTART;TZID=America/Montreal:20090601T150000
       DTEND;TZID=America/Montreal:20090601T160000

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    RFC 6638                    CalDAV Scheduling                  June 2012

       RRULE:FREQ=DAILY;INTERVAL=1;COUNT=5
       EXDATE;TZID=America/Montreal:20090603T150000
       TRANSP:OPAQUE
       SUMMARY:Review Internet-Draft
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
        mailto:cyrus@example.com
       ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
        ACCEPTED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
        e.net
       END:VEVENT
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090603T183823Z
       RECURRENCE-ID;TZID=America/Montreal:20090602T150000
       DTSTART;TZID=America/Montreal:20090602T150000
       DTEND;TZID=America/Montreal:20090602T160000
       TRANSP:TRANSPARENT
       SUMMARY:Review Internet-Draft
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Cyrus Daboo";CUTYPE=INDIVIDUAL;PARTSTAT=ACCEPTED:
        mailto:cyrus@example.com
       ATTENDEE;CN="Bernard Desruisseaux";CUTYPE=INDIVIDUAL;PARTSTAT=
        DECLINED;ROLE=REQ-PARTICIPANT;RSVP=TRUE:mailto:bernard@exampl
        e.net
       END:VEVENT
       END:VCALENDAR

       Bernard's deletion of a recurrence instance will cause his server to
       deliver a scheduling message to Cyrus.  Cyrus's client will find the
       following reply message from Bernard in Cyrus's scheduling Inbox
       collection:

       >> Request <<

       GET /home/cyrus/calendars/inbox/6504923FD3AD.ics HTTP/1.1
       Host: cal.example.com

       >> Response <<

       HTTP/1.1 200 OK
       Date: Tue, 02 Jun 2009 18:52:58 GMT
       Last-Modified: Tue, 02 Jun 2009 18:52:58 GMT
       ETag: "eb897deabc8939589da116714bc99265"
       Content-Type: text/calendar; charset="utf-8"
       Content-Length: xxxx

    Daboo & Desruisseaux         Standards Track                   [Page 76]

    RFC 6638                    CalDAV Scheduling                  June 2012

       BEGIN:VCALENDAR
       VERSION:2.0
       PRODID:-//Example Corp.//CalDAV Client//EN
       METHOD:REPLY
       BEGIN:VTIMEZONE
       TZID:America/Montreal
       BEGIN:STANDARD
       DTSTART:20071104T020000
       RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
       TZNAME:EST
       TZOFFSETFROM:-0400
       TZOFFSETTO:-0500
       END:STANDARD
       BEGIN:DAYLIGHT
       DTSTART:20070311T020000
       RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
       TZNAME:EDT
       TZOFFSETFROM:-0500
       TZOFFSETTO:-0400
       END:DAYLIGHT
       END:VTIMEZONE
       BEGIN:VEVENT
       UID:9263504FD3AD
       SEQUENCE:0
       DTSTAMP:20090603T183823Z
       RECURRENCE-ID;TZID=America/Montreal:20090603T150000
       DTSTART;TZID=America/Montreal:20090603T150000
       DTEND;TZID=America/Montreal:20090603T160000
       SUMMARY:Review Internet-Draft
       ORGANIZER;CN="Cyrus Daboo":mailto:cyrus@example.com
       ATTENDEE;CN="Bernard Desruisseaux";PARTSTAT=DECLINED:
        mailto:bernard@example.net
       REQUEST-STATUS:2.0;Success
       END:VEVENT
       END:VCALENDAR

    Daboo & Desruisseaux         Standards Track                   [Page 77]

    RFC 6638                    CalDAV Scheduling                  June 2012

    Authors' Addresses

       Cyrus Daboo
       Apple Inc.
       1 Infinite Loop
       Cupertino, CA  95014
       USA

       EMail: cyrus@daboo.name
       URI:   http://www.apple.com/

       Bernard Desruisseaux
       Oracle Corporation
       600 Blvd. de Maisonneuve West
       Suite 1900
       Montreal, QC  H3A 3J2
       CANADA

       EMail: bernard.desruisseaux@oracle.com
       URI:   http://www.oracle.com/

    Daboo & Desruisseaux         Standards Track                   [Page 78]