Calendaring Extensions to WebDAV (CalDAV)

Definitions of XML elements in this document use XML element type declarations (as found in XML Document Type Declarations), described in Section 3.2 of [8].¶

The namespace "urn:ietf:params:xml:ns:caldav" is reserved for the XML elements defined in this specification, or in other Standards Track IETF RFCs written to extend CalDAV. It MUST NOT be used for proprietary extensions.¶

Note that the XML declarations used in this document are incomplete, in that they do not include namespace information. Thus, the reader MUST NOT use these declarations as the only way to create valid CalDAV properties or to validate CalDAV XML element type. Some of the declarations refer to XML elements defined by WebDAV which use the "DAV:" namespace. Wherever such elements appear, they are explicitly given the "DAV:" prefix to help avoid confusion.¶

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

The augmented BNF used by this document to describe protocol elements is described in Section 2.1 of [4]. Because this augmented BNF uses the basic production rules provided in Section 2.2 of [4], those rules apply to this document as well.¶

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 [1].¶

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 string "DAV:" and "CALDAV:" will be prefixed to the element types respectively.¶

A "precondition" of a method describes the state of the server that must be true for that method to be performed. A "postcondition" of a method describes the state of the server that must be true after that method has been completed. If a method precondition or postcondition for a request is not satisfied, the response status of the request MUST be either 403 (Forbidden) if the request should not be repeated because it will always fail, or 409 (Conflict) if it is expected that the user might be able to resolve the conflict and resubmit the request.¶

In order to allow better client handling of 403 and 409 responses, a distinct XML element type is associated with each method precondition and postcondition of a request. When a particular precondition is not satisfied or a particular postcondition cannot be achieved, the appropriate XML element MUST be returned as the child of a top-level DAV:error element in the response body, unless otherwise negotiated by the request. In a 207 Multi-Status response, the DAV:error element would appear in the appropriate DAV:responsedescription element.¶

A CalDAV server is a calendaring-aware engine combined with a WebDAV repository. A WebDAV repository is a set of WebDAV collections, containing other WebDAV resources, within a unified URL namespace. For example, the repository "http://example.org/webdav/" may contain WebDAV collections and resources, all of which have URLs beginning with "http://example.org/webdav/". Note that the root URL "http://example.org/" may not itself be a WebDAV repository (for example, if the WebDAV support is implemented through a servlet or other Web server extension).¶

A WebDAV repository may include calendar data in some areas, and non-calendaring data in other areas.¶

A WebDAV repository may advertise itself as a CalDAV server if it supports the functionality defined in this specification at any point within the root of the repository. That might mean that calendaring data is spread throughout the repository and mixed with non-calendar data in nearby collections (e.g., calendar data may be found in /lisa/calendar/ as well as in /bernard/calendar/, and non-calendar data in /lisa/contacts/). Or, it might mean that calendar data can be found only in certain sections of the repository (e.g., /calendars/user/). Calendaring features are only required in the repository sections that are or contain calendaring objects. So a repository confining calendar data to the /caldav/ collection would only need to support the CalDAV required features within that collection.¶

The CalDAV server or repository is the canonical location for calendar data and state information. Both CalDAV servers and clients MUST ensure that the data is consistent and compliant. Clients may submit requests to change data or download data. Clients may store calendar objects offline and attempt to synchronize at a later time. However, clients MUST be prepared for calendar data on the server to change between the time of last synchronization and when attempting an update, as calendars may be shared and accessible via multiple clients. HTTP ETags and other tools help this work.¶

Recurrence is an important part of the data model because it governs how many resources are expected to exist.¶

Consider the outcome if recurrence were handled through the creation of many nearly-identical WebDAV resources. With this model, it becomes hard to keep synchronized data consistent. Even worse, some features like LOCK become difficult -- it's hard to lock the right set of resources so that the user can change the title of all recurrences of an appointment. Due to these considerations, this proposal does not model recurrences as separate resources.¶

Instead, this proposal models recurrence patterns as properties of calendar resources. This makes for much less data to synchronize, and makes it easier to make changes to all recurrences or to a recurrence pattern. It makes it easier to create a recurring component, and easier to delete all recurrences.¶

The drawback of the recurrence-is-a-property approach is that it becomes harder to see what events occur in a given time interval. It's a very common function for calendar views to display all events happening between midnight yesterday and midnight tonight, or all events happening within one week. In these views, each recurrence appears as if it were an individual appointment. The CALDAV:calendar-query REPORT defined in this document make these views possible.¶

Because of this choice, clients MUST NOT create separate resources to represent a recurring event when the recurrence pattern is known. Otherwise, it makes it more difficult for other clients to interoperate and modify the recurring event. Most importantly, clients MUST NOT duplicate events represented through recurrence patterns with manually created events, which would appear as duplicates to the server and to other clients.¶

Calendar resources in CalDAV MUST be valid iCalendar objects. As such, an individual VTIMEZONE calendar component MUST be specified for each unique TZID parameter value specified in an iCalendar object. Unfortunately this mean that the same VTIMEZONE component will get sent or retrieved multiple times for each iCalendar object that uses the timezone. This is not efficient in terms of bandwidth usage.¶

[rfc.comment.2: Not clear how big an issue that really is. CalDAV already allows clients to retrieve iCalendar objects without their VTIMEZONE component with the CALDAV:calendar-query REPORT. It is still not clear whether a client could rely only on the value of the TZID parameter, or should it always requests a VTIMEZONE component with at least the TZID and TZURL properties and rely on the TZURL as a unique identifier for a given time zone. CalDAV servers have no choice but to return complete VTIMEZONE components in iCalendar object retrieve with the GET method as their is no way to know if the client is a CalDAV client or a simple HTTP client. On a PUT request perhaps a CalDAV server could accept an iCalendar object with a VTIMEZONE object that has at least TZURL that points to a calendar resource that defines a time zone on the server. --desruisseaux] ¶

The timezone collection is a calendar collection that contains only VTIMEZONE components as separate resources within that collection. There MUST be only one VTIMEZONE component per calendar resource in the timezone collection. Clients can discover the location of the timezone collection with the CALDAV:timezone-collection-set OPTIONS request (see Section 5.2.4) and can list the supported timezones and retrieve specific timezone component data by using the CALDAV:calendar-query REPORT defined in Section 8.3.¶

A calendar collection contains resources that represent the iCalendar objects within a calendar. A calendar collection may be created through provisioning (e.g., automatically created when a user's account is created), or it may be created through MKCALENDAR. This can be useful for a user to create a second calendar (e.g., soccer schedule) or for users to share a calendar (e.g., team events or conference room). Note however that this document doesn't define what extra calendars are for, users must rely on non-standard cues to find out what a calendar is for, or use the CALDAV:calendar-description property defined in Section 6.1 to provide such a cue.¶

Calendar collections MUST NOT contain other calendar collections. Multiple calendars MAY be children of the same WebDAV collection.¶

A calendar collection MAY contain additional collections and non-collection resources of types not defined here. How such items are used is not defined by this specification. However, additional collections contained in a calendar collection MUST NOT contain calendar collections.¶

Each top-level iCalendar component within the VCALENDAR component is represented as a separate WebDAV resource, with the following exceptions ¶

• sets of recurring items (i.e., components with the same UID iCalendar property value, but differing RECURRENCE-ID values) are all stored in the same resource. That is, each WebDAV resource MUST only contain iCalendar components with the same iCalendar UID property value, and all iCalendar components with the same iCalendar UID property value MUST be stored in the same WebDAV resource.
• any top-level component that references a timezone via a "TZID" property MUST include the VTIMEZONE component corresponding to that timezone id, as required by iCalendar, unless the timezone is one included in the server's timezone collection, as described in Section 3.3.

For example, given the following iCalendar object: ¶

BEGIN:VCALENDAR
CALSCALE:GREGORIAN 
PRODID:-//Example, Inc.\, Inc.//Example App//EN
VERSION:2.0 
BEGIN:VEVENT
UID:[email protected]
SUMMARY:One-off Meeting 
DTSTAMP:20041210T183904Z
DTSTART:20041207T120000Z 
DTEND:20041207T130000Z
END:VEVENT
BEGIN:VEVENT 
UID:[email protected]
SUMMARY:Weekly Meeting 
DTSTAMP:20041210T183838Z
DTSTART:20041206T120000Z 
DTEND:20041206T130000Z
RRULE:FREQ=WEEKLY
END:VEVENT 
BEGIN:VEVENT
UID:[email protected] 
RECURRENCE-ID:20041213T120000Z
DTSTAMP:20041210T183838Z 
DTSTART:20041213T130000Z
END:VEVENT
END:VCALENDAR 
          

The VEVENT with UID value "[email protected]", would be stored in its own unique WebDAV resource. The two VEVENTs with UID value "[email protected]", which represent a set of recurring events where one instance has been overridden, would be stored in a single unique WebDAV resource.¶

A MKCALENDAR request creates a new calendar collection resource. A server MAY restrict calendar collection creation to particular collections, but a client can determine the location of these collections from a CALDAV:calendar-collection-set OPTIONS request (see Section 5.2.2).¶

Support for MKCALENDAR on the server is OPTIONAL because some calendar stores only support one calendar per user (or principal) and those are typically pre-created for each account. However, servers and clients are strongly encouraged to support MKCALENDAR whenever possible to allow users to create multiple calendars to better help organize their data.¶

Clients SHOULD use the DAV:displayname property for a human-readable name of the calendar. This requires the clients to issue a PROPPATCH request to change the DAV:displayname property to the appropriate value immediately after issuing the MKCALENDAR request. When displaying calendars to users, clients SHOULD check the DAV:displayname property and use that value as the name of the calendar. In the event that the DAV:displayname property is empty, the client MAY use the last part of the calendar-collection URI as the name.¶

If a MKCALENDAR request fails, the server state preceding the request MUST be restored.¶

Marshalling:¶

• If a request body is included, it MUST be a CALDAV:mkcalendar XML element.

  <!ELEMENT mkcalendar ANY>
  

• If a response body for a successful request is included, it MUST be a CALDAV:mkcalendar-response XML element.

  <!ELEMENT mkcalendar-response ANY>
  

• The response MUST include a Cache-Control:no-cache header.

Preconditions: ¶

• (DAV:resource-must-be-null): A resource MUST NOT exist at the Request-URI.
• (CALDAV:calendar-collection-location-ok): The Request-URI MUST identify a location where a calendar collection can be created.
• (CALDAV:insufficient-privilege): The DAV:bind privilege MUST be granted to the current authenticated user.

Postconditions: ¶

• (CALDAV:initialize-calendar-collection): A new calendar collection exists at the Request-URI. The DAV:resourcetype of the calendar collection MUST be DAV:collection. Additionally, a calendar collection MUST report the CALDAV:calendar XML element in the value of the DAV:resourcetype property.

Clients typically populate calendars with calendar resources. The URL for each calendar resource is entirely arbitrary, and does not need to bear a specific relationship (but might) to the calendar resource's subject, scheduled time, UID or other metadata. A new calendar resource must have a new URL, otherwise the new component would instead be an update to an existing calendar resource.¶

When servers create new resources, it's not hard for the server to choose a unique URL. It's slightly tougher for clients, because a client might not want to examine all resources in the collection, and might not want to lock the entire collection to ensure that a new one isn't created with a name collision. However, there are tools to mitigate this. If the client intends to create a new non-collection resource, such as a new VEVENT, the client SHOULD use the HTTP header "If-None-Match: *" on the PUT request. The Request-URI on the PUT request MUST include the target collection, where the resource is to be created, plus the name of the resource in the last path segment. The last path segment could be a random number, or it could be a sequence number, or a string related to the object's 'summary' property. No matter how the name is chosen, the "If-None-Match" header ensures that the client cannot overwrite an existing resource even if it has accidentally chosen a duplicate resource name.¶

Servers SHOULD return an ETag header containing the actual ETag of the newly created resource on a successful creation.¶

>> Request <<

PUT /lisa/calendar/newevent.ics HTTP/1.1
If-None-Match: *
Host: cal.example.com
Content-Type: text/calendar
Content-Length: xxx

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Example Corp.//CalDAV Client//EN
BEGIN:VEVENT
UID:[email protected]
DTSTART:20010714T170000Z
DTEND:20010715T035959Z
SUMMARY:Bastille Day Party
END:VEVENT
END:VCALENDAR

>> Response <<

HTTP/1.1 201 Created
Date: Thu, 02 Sep 2004 16:53:32 GMT
Location: http://cal.example.com/lisa/calendar/ev1234.ics
Content-Length: 0
ETag: "123456789-000-111"

The request to change an existing event is the same, but with a specific ETag in the "If-Match" header, rather than the "If-None-Match" header.¶

As mentionned in Section 3.10 of RFC 2445 [2], the URI of calendar resources containing (an arbitrary set of) calendaring and scheduling information may be suffixed by ".ics", and the URI of calendar resources containing free or busy time information may be suffixed by ".ifb".¶

A CalDAV server MAY return the Location header in a 201 (Created) response to a PUT request if the server created the resource at a different URI than the Request-URI. CalDAV clients MUST be able to handle the URI returned by the server in the Location header, by adjusting their original resource URI to the new one returned by the server.¶

Name:

calendar-description

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Provides a description for the resource that is suitable for presentation to a user.

Description:

The CALDAV:calendar-description property MAY be defined on all calendar collection resources. If present, the property contains a description of the resource that is suitable for presentation layer.

A CalDAV server MUST support WebDAV ACL [7]. WebDAV ACL provides a framework for an extensible list of privileges on WebDAV collections and ordinary resources. A CalDAV server MUST also support the calendaring privilege defined in this section.¶

This section defines a new property for WebDAV principal resources as defined in RFC3744 [7].¶

The REPORT method (defined in Section 3.6 of RFC3253 [5]) provides an extensible mechanism for obtaining information about a resource. Unlike the PROPFIND method, which returns the value of one or more named properties, the REPORT method can involve more complex processing. REPORT is valuable in cases where the server has access to all of the information needed to perform the complex request (such as a query), and where it would require multiple requests for the client to retrieve the information needed to perform the same request.¶

A server that supports calendar-access MUST support the DAV:expand-property report (defined in Section 3.8 of RFC3253 [5]).¶

A WebDAV collection which contains one or more calendar collections is not a new type of resource, but it may support these new REPORT. If so, then the REPORT is expected to have the semantics of including information from all the calendar data contained in the collection, and its children, recursively. These collections may contain more than only calendar related resources. It's up to the server, if it supports this REPORT on a normal WebDAV collection, to find calendar resources and decide what to do with non-calendar resources and whether those may also appear in the collection or its children.¶

If these reports are supported on ordinary collections the server advertises the capability with the DAV:supported-report-set property as already described.¶

The CALDAV:calendar-query REPORT performs a search for all calendar resources (e.g., iCalendar objects) that match a specified search filter. The response of this report will contain all the WebDAV properties and calendar resource data specified in the request. In the case of the CALDAV:calendar-data XML element, one can explicitly specify the calendar components and properties that should be returned in the calendar resource data that matches the search filter.¶

The format of this report is modeled on the PROPFIND method. The request and response bodies of the CALDAV:calendar-query report use XML elements that are also used by PROPFIND. In particular the request can include XML elements to request WebDAV properties to be returned. When that occurs the response should follow the same behavior as PROPFIND with respect to the DAV:multistatus response elements used to return specific property results. For instance, a request to retrieve the value of a property which does not exist is an error and MUST be noted with a response XML element which contains a 404 (Not Found) status value.¶

Support for the calendar-query REPORT is REQUIRED.¶

Marshalling: ¶

• The request body MUST be a CALDAV:calendar-query XML element as defined in Section 10.1.
• The response body for a successful request MUST be a DAV:multistatus XML element (i.e., the response uses the same format as the response for PROPFIND). In the case where there are no response elements, the returned multistatus XML element is empty.
• The response body for a successful calendar-query REPORT request MUST contain a DAV:response element for each iCalendar object that matched the search filter. The declaration of the DAV:response element from Section 12.9.1 of RFC2518 [3] has been modified as follow to allow the CALDAV:calendar-data element within the DAV:response element, see Section 10.5

[rfc.comment.4: We need to define the role of the Depth request header when applied to a collection resource. We need to specify preconditions and postconditions. (e.g., DAV:number-of-matches-within-limits). --desruisseaux] ¶

The CALDAV:calendar-multiget REPORT is used to retrieve specific calendar resources from within a collection, if the Request-URI is a collection, or to retrieve a specific calendar resource, if the Request-URI is a calendar resource. This report is similar to the CALDAV:calendar-query REPORT (see Section 8.3), except that it takes a list of DAV:href elements instead of a CALDAV:filter element to determine which calendar resources to return.¶

Support for the calendar-multiget REPORT is REQUIRED.¶

Marshalling: ¶

• The request body MUST be a CALDAV:calendar-multiget XML element (see Section 10.6, which MUST contain at least one DAV:href XML element, and one optional CALDAV:calendar-data element as defined in Section 10.2. If the Request-URI is a collection resource, then the DAV:href elements MUST refer to resources within that collection, and they MAY refer to resources at any depth within the collection. As a result the "Depth" header MUST be ignored by the server and SHOULD NOT be sent by the client. If the Request-URI refers to a non-collection resource, then there MUST be a single DAV:href element that is equal to the Request-URI.
• The response body for a successful request MUST be a DAV:multistatus XML element. In the case where there are no response elements, the returned multistatus XML element is empty.
• The response body for a successful CALDAV:calendar-multiget REPORT request MUST contain a DAV:response element for each calendar resource referenced by the provided set of DAV:href elements. The DAV:response element is as defined in Section 10.5.
• In the case of an error accessing any of the provided DAV:href resources, the server MUST return the appropriate error status code in the DAV:status element of the corresponding DAV:response element.

The CALDAV:free-busy-query REPORT generates an iCalendar VFREEBUSY component containing free busy information for all relevant components within calendar collections which have the CALDAV:view-free-busy or DAV:read privilege granted for the current authenticated user.¶

Only the VEVENT components, with the TRANSP property set to a value different from "TRANSPARENT", and the VFREEBUSY components will be considered to generate the free busy time information.¶

Support for the CALDAV:free-busy-query REPORT is REQUIRED.¶

Marshalling: ¶

• The request body MUST be a CALDAV:free-busy-query XML element (see Section 10.7, which MUST contain at least one CALDAV:time-range XML element, as defined in Section 10.4.
• The response body for a successful request MUST be a DAV:multistatus XML element. In the case where there are no response elements, the returned multistatus XML element is empty.
• The response body for a successful CALDAV:free-busy-query REPORT request MUST contains a DAV:response element for each calendar collection for which free-busy information has been computed. Each DAV:response element contains a single CALDAV:calendar-data XML element as defined in Section 10.2. The CALDAV:calendar-data XML element MUST contain an iCalendar object with a single VFREEBUSY component, with zero or more FREEBUSY property values that describe the busy time intervals for the calendar resources being targeted, and with other properties set according to the rules of iCalendar. This report only returns busy time information. Applications desiring free time information MUST infer this from available busy time information.

When the Request-URI for a CALDAV:free-busy-query REPORT is a calendar collection, the free-busy data is implicitly determined from the "text/calendar" VEVENT resources within the calendar collection, irrespective of the value of any Depth header included in the REPORT request. Only calendar resources containing VEVENT or VFREEBUSY components that have the CALDAV:view-free-busy privilege granted to the current authenticated user will be computed in the response.¶

When the Request-URI for a CALDAV:free-busy-query REPORT is a non-calendar collection, the scope of the report is governed by the value of the Depth header in the request as follows: ¶

• 'Depth: 0' - an empty VFREEBUSY component will be returned as there is no valid calendar data to be scanned on the collection.
• 'Depth: 1' - free-busy data for any calendar collections immediately within the target collection is returned.
• 'Depth: infinity' - free-busy data for all calendar collections within any sub-collections of the target collection is returned.

Clients may not need all the properties in a calendar component when presenting information to the user. Since some property data can be large (e.g., 'ATTACH' or 'ATTENDEE' lists) clients can choose to ignore those by only requesting the specific items it knows it will use, through use of the CALDAV:calendar-data XML element in the relevant reports.¶

However, if a client needs to make a change to a component, it can only change the entire component data via a PUT request. There is no way to incrementally make a change to a set of properties within a calendar component resource. As a result the client will have to cache the entire set of properties on a resource that is being changed.¶

Clients should use the set of timezone components in the server's timezone collection advertises in the namespace report, for any timezones for calendar components that it creates. This avoids the need for the client or server to send the timezone data along with the component data and thus reduces network bandwidth usage.¶

Name:

calendar-query

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Defines a report for querying calendar data

Description

See Section 8.3.

Name:

calendar-data

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Used to define which parts of a calendar component object should be returned by the report that uses this element.

Description:

When used in a request, the CALDAV:calendar-data element specifies the iCalendar components and properties to be returned in the iCalendar objects part of the response. If this element doesn't contain any CALDAV:comp element, iCalendar objects will be returned with all their components and properties.

Value:

When used inside a response, the CALDAV:calendar-data element contains an iCalendar object that matched the search filter specified in the request.

Name:

filter

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Determines which matching components are returned.

Description:

The "filter" element specifies the search filter used to match components that should be returned by a report.

Name:

time-range

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

Specifies a time interval for testing components against.

Description:

The CALDAV:time-range element allows for a single time range to be defined, in order to limit all the results of the search to the set of resources that contain a component which falls into that time range. The value of the "start" and "end" attributes MUST follow the syntax of the DATE or DATE-TIME iCalendar value type, with any time specified in UTC.

A VEVENT component falls in a given time-range if:

(DTSTART <= start AND DTEND > start) OR
(DTSTART <= start AND DTSTART+DURATION > start) OR
(DTSTART >= start AND DTSTART < end) OR
(DTEND   > start AND DTEND <= end)
      

A VTODO component falls in a given time-range if:

(DTSTART <= start AND DUE >= start) OR
(DTSTART <= start AND DTSTART+DURATION > start) OR
(DTSTART >= start AND DTSTART < end) OR
(DUE     >= start AND DUE < end)
      

A VJOURNAL component falls in a given time-range if:

DTSTART >= start AND DTSTART < end
      

A VALARM component falls in a given time-range if:

trigger-time >= start AND trigger-time < end
      

Any property of value type DATE-TIME or DATE (e.g., DTSTAMP) will match a given time-range if:

value >= start AND value < end
      

Name:

response

Namespace:

DAV:

Purpose:

Response that includes calendar data.

Description:

Modifies the standard WebDAV response element to include calendar data in the response if required by the report type.

Name:

calendar-multiget

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

CalDAV report used to retrieve specific calendar component items via their URIs.

Description:

See Section 8.4.

Name:

free-busy-query

Namespace:

urn:ietf:params:xml:ns:caldav

Purpose:

CalDAV report used to generate a VFREEBUSY to determine busy time over a specific set of time ranges.

Description:

See Section 8.5.

CalDAV relies on HTTP authentication to authenticate users to the server. As a result the security considerations for use of HTTP authentication also apply to CalDAV. In particular, the HTTP Basic authentication method MUST NOT be used without adequate transport layer security.¶

Servers MUST take adequate precautions to ensure malicious clients cannot consume excessive server resources (CPU, memory, disk, etc.) through carefully crafted reports. For example, a client could upload an event with a recurrence rule that specifies a recurring event occurring every second for the next 100 years which would result in approximately 3 x 10^9 instances! A report that asks for recurrences to be expanded over that range would likely constitute a denial-of-service attack on the server.¶

[rfc.comment.6: We should make an explicit reference to the security considerations mentionned in iCalendar, iTIP and iMIP. We should also specify if there is any semantic defined in CalDAV for the iCalendar property CLASS (access classification). --desruisseaux] ¶

URI: urn:ietf:params:xml:ns:caldav¶

Registrant Contact: See the "Author's Address" section of this document.¶

XML: None. Namespace URIs do not represent an XML specification.¶

1. Removed a lot of non-normative text.
2. Removed property promotion/demotion requirements.
3. Removed calendar-owner and cal-scale properties.
4. Removed 'ical' prefix/text from element names.
5. Relaxed WebDAV Class 2 (locking) requirement to a MAY.
6. Relaxed MKCALENDAR requirement to a SHOULD.
7. Moved the XML Namespace section in the Introduction.
8. Added CALDAV: prefix to CalDAV XML elements in the text.
9. Added CALDAV:calendar-multiget report.
10. Added CALDAV:free-busy-query report.
11. Added CALDAV:calendar-description property.
12. Changed CALDAV:calendar-query-result element name to CALDAV:calendar-data
13. Added description and examples of handling timezones.
14. Added mandatory "start" and "end" attributes to the CALDAV:expand-recurrence-set element.
15. Added three CalDAV OPTIONS requests.
16. Grouped XML Element declarations in a separate section.

1. Added a note about the HTTP Location response header.
2. Added report calendar-query.
3. Removed reports calendar-property-search and calendar-time-range.
4. Removed section on CalDAV and timezones.
5. Added requirement to return ETag on creation.
6. Revised data model to remove sub-collections from calendar collection.
7. Added informative references section.
8. Removed dependencies on DASL.

1. Removed Calendar Containers (simplification that doesn't seem to remove much functionality)
2. Added MKCALENDAR to create calendars and all sub-collections
3. Added cal-scale property to calendars

Basically still adding major sections of content: ¶

1. Defined new field values to the OPTIONS "DAV:" response header
2. Added new resource properties
3. Added new principal properties
4. Added new SCHEDULE method and related headers
5. Added new privileges for scheduling

1. Added section on privileges for calendaring, extending WebDAV ACL privilege set
2. Defined what to do with unrecognized properties in the bodies of iCalendar events, with respect to property promotion/demotion