Internet DRAFT - draft-daboo-valarm-extensions
draft-daboo-valarm-extensions
Network Working Group C. Daboo
Internet-Draft Apple
Intended status: Standards Track May 3, 2011
Expires: November 4, 2011
VALARM Extensions for iCalendar
draft-daboo-valarm-extensions-03
Abstract
This document defines a set of extensions to the iCalendar VALARM
component to enhance use of alarms and improve interoperability
between clients and servers.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on November 4, 2011.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Extensible syntax for VALARM . . . . . . . . . . . . . . . . . 3
4. VALARM Unique Identifier . . . . . . . . . . . . . . . . . . . 5
5. VALARM URI Action . . . . . . . . . . . . . . . . . . . . . . 6
6. VALARM Agent Property . . . . . . . . . . . . . . . . . . . . 7
6.1. Alarm Agent Property . . . . . . . . . . . . . . . . . . . 7
6.2. ID Property Parameter . . . . . . . . . . . . . . . . . . 9
6.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 9
7. VALARM Acknowledged Property . . . . . . . . . . . . . . . . . 9
7.1. Acknowledged Property . . . . . . . . . . . . . . . . . . 10
7.2. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 11
8. Snoozing Alarms . . . . . . . . . . . . . . . . . . . . . . . 11
9. VALARM Proximity Trigger Property . . . . . . . . . . . . . . 11
9.1. Proximity Property . . . . . . . . . . . . . . . . . . . . 12
9.2. Geo Location Property . . . . . . . . . . . . . . . . . . 13
9.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 14
10. Default Alarms in CalDAV . . . . . . . . . . . . . . . . . . . 14
11. Security Considerations . . . . . . . . . . . . . . . . . . . 15
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
12.1. Property Registrations . . . . . . . . . . . . . . . . . . 16
12.2. Parameter Registrations . . . . . . . . . . . . . . . . . 16
12.3. Actions Registry . . . . . . . . . . . . . . . . . . . . . 16
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
14.1. Normative References . . . . . . . . . . . . . . . . . . . 17
14.2. Informative References . . . . . . . . . . . . . . . . . . 17
Appendix A. Change History (To be removed by RFC Editor
before publication) . . . . . . . . . . . . . . . . . 17
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 18
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1. Introduction
The iCalendar [RFC5545] specification defines a set of components
used to describe calendar data. One of those is the "VALARM"
component which appears as a sub-component of "VEVENT" and "VTODO"
components. The "VALARM" component is used to specify a reminder for
an event or to-do. Different alarm actions are possible, as are
different ways to specify how the alarm is triggered.
As iCalendar has become more widely used and as client-server
protocols such as CalDAV [RFC4791] have become more popular, several
issues with "VALARM" components have arisen. Most of these relate to
the need to extend the existing "VALARM" component with new
properties and behaviors to allow clients and servers to accomplish
specific tasks in an interoperable manner. For example, clients
typically need a way to specify that an alarm has been dismissed by a
calendar user, or has been "snoozed" by a set amount of time. To
date, this has been done through the use of custom "X-" properties
specific to each client implementation, leading to poor
interoperability.
This specification defines a set of extensions to "VALARM" components
to cover common requirements for alarms not currently addressed in
iCalendar. Each extension is defined in a separate section below.
For the most part, each extension can be supported independently of
the others, though in some cases one extension will require another.
In addition, this specification describes mechanisms by which clients
can interoperably implement common features such as "snoozing".
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
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 type names respectively.
3. Extensible syntax for VALARM
Section 3.6.6 of [RFC5545] defines the syntax for "VALARM" components
and properties within them. However, as written, it is hard to
extend this by adding, e.g., a new property common to all types of
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alarm. Since many of the extensions defined in this document need to
extend the base syntax, an alternative form for the base syntax is
defined here, with the goal of simplifying specification of the
extensions.
A "VALARM" calendar component is re-defined by the following
notation:
alarmcext = "BEGIN" ":" "VALARM" CRLF
alarmprop
"END" ":" "VALARM" CRLF
alarmprop = *(
; the following are REQUIRED,
; but MUST NOT occur more than once
action / trigger /
; one set of action properties MUST be
; present and MUST match the action specified
; in the ACTION property
actionprops /
; the following is OPTIONAL,
; and MAY occur more than once
x-prop / iana-prop
)
actionprops = audiopropext / disppropext / emailpropext
audiopropext = *(
; 'duration' and 'repeat' are both OPTIONAL,
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
duration / repeat /
; the following is OPTIONAL,
; but MUST NOT occur more than once
attach
)
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disppropext = *(
; the following are REQUIRED,
; but MUST NOT occur more than once
description /
; 'duration' and 'repeat' are both OPTIONAL,
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
duration / repeat
)
emailpropext = *(
; the following are all REQUIRED,
; but MUST NOT occur more than once
description / summary /
; the following is REQUIRED,
; and MAY occur more than once
attendee /
; 'duration' and 'repeat' are both OPTIONAL,
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
duration / repeat
)
4. VALARM Unique Identifier
Several of the other extensions in this specification require
identifying a specific instance of a "VALARM" component in an
iCalendar stream. To aid that, this extension adds a "UID" property
to "VALARM" components to allow a unique identifier to specified.
The value of this property can then be used to refer uniquely to the
"VALARM" component.
The "UID" property defined here follows the definition in Section
3.8.4.7 of [RFC5545]. In particular it MUST be a globally unique
identifier.
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The "VALARM" component defined in Section 3 is extended here as:
alarmprop /= *(
; the following is OPTIONAL,
; but MUST NOT occur more than once
uid
)
5. VALARM URI Action
Currently "VALARM" components have actions for audio, display and
email. New types of action are of interest, e.g., SMS, instant
messaging, etc. Rather then specify separate actions for these, an
alternative is to define a "URI" action that allows any URI scheme to
be used as an action, where it makes sense. Thus URI schemes for IM
[RFC3860], SIP [RFC3261], TEL [RFC3966] etc could be used.
This extension defines a new "URI" property value for use with the
"ACTION" property in "VALARM" components. A new set of action
properties is defined for "VALARM" components based on this new
action as defined by the syntax below.
actionvalue /= "URI"
; Adds a new action for a "VALARM"
actionprop /= uriprop
; Re-defines the "VALARM" component to include
; "uriprop" as a new set of action properties
uriprop = *(
; the following is REQUIRED,
; and MUST occur only once
uri /
; 'duration' and 'repeat' are both OPTIONAL,
; and MUST NOT occur more than once each,
; but if one occurs, so MUST the other
duration / repeat
)
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6. VALARM Agent Property
With the advent of a standard client/server protocol for calendaring
and scheduling data ([RFC4791]) there is a need to specify which
client or server should handle the presentation of an alarm when it
is triggered. For example, calendar users want to be able to receive
alarms at all times, even when their desktop client might be
unavailable. Since the server is "always on", a service running on
the server could monitor alarm status and, when appropriate, trigger
those alarms. In addition it may be important for only the server or
the client to be set to handle an alarm - and in some cases only
specific servers or clients.
To address this need, this specification defines an "ALARM-AGENT"
iCalendar property that can be added to any "VALARM" component. This
property specifies whether a client or server or both should be
responsible for processing the alarm when it triggers. In addition,
a "ID" property parameter can be added to uniquely identify the
client or server that should process the alarm. This is defined by
the syntax below.
alarmprop /= *(
; the following is OPTIONAL,
; and MAY occur more than once
alarm-agent
)
6.1. Alarm Agent Property
Property Name: ALARM-AGENT
Purpose: This property specifies whether a client, server, both or
none gets to process an alarm when it is triggered.
Value Type: TEXT
Property Parameters: IANA, non-standard, and id property parameters
can be specified on this property.
Conformance: This property can be specified within "VALARM" calendar
components.
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Description: This property is used to specify who is responsible for
processing an alarm when it is triggered. When the value "SERVER"
is specified, only a server that has a copy of the event is
responsible. When the value "CLIENT" is specified, only a client
that has a copy of the event is responsible. When the value
"BOTH" is specified, either a client or server is responsible.
When the value "NONE" is specified, neither a client nor server is
responsible (i.e., the alarm action is never carried out when it
triggers).
If the "ID" property parameter is specified for "SERVER" or
"CLIENT" values, then only the client or server identified by the
"ID" value is responsible. Clients or servers that are not
responsible for the alarm SHOULD NOT process the alarm action when
it is triggered. If multiple clients or servers need to be
specified, then the "ALARM-AGENT" property should be included
multiple times in the "VALARM" component, with each one containing
the appropriate "ID" property parameter value to identify each
client or server.
In the absence of this property clients and servers can choose to
process the alarm themselves as appropriate. i.e., a default value
of "BOTH".
This property MAY occur more than once to allow multiple
processors of an alarm.
Format Definition: This property is defined by the following
notation:
alarm-agent = "ALARM-AGENT" alarmagentparam ":"
alarmagentvalue CRLF
alarmagentparam = *(
; the following is OPTIONAL,
; but MUST NOT occur more than once
(";" idparam) /
; the following is OPTIONAL,
; and MAY occur more than once
(";" other-param)
)
alarmagentvalue = "SERVER" / "CLIENT" / "BOTH" / "NONE" /
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iana-token / x-name
Example: The following are examples of this property:
ALARM-AGENT:SERVER
ALARM-AGENT;ID="tag:example.com,2011:cyrus-desktop":CLIENT
6.2. ID Property Parameter
Parameter Name: ID
Purpose: This property parameter specifies a URI identifier for the
property it is applied to.
Format Definition: This property parameter is defined by the
following notation:
idparam = "ID" "=" DQUOTE uri DQUOTE
Description: This property parameter is used to specify a URI
identifier that is associated with the property it is applied to.
Each property that allows this parameter to be specified MUST
indicate what the value of the URI represents.
Example: The following is an example of this property parameter:
ALARM-AGENT;ID="http://calendar.example.com":SERVER
6.3. Examples
TODO Example of VALARM components
7. VALARM Acknowledged Property
There is currently no way for a "VALARM" component to indicate
whether it has been triggered and acknowledged or not. With the
advent of a standard client/server protocol for calendaring and
scheduling data ([RFC4791]) it is quite possible for an event with an
alarm to exist on multiple clients in addition to the server. If
each of those is responsible for performing the action when an alarm
triggers then multiple "alerts" are generated by different devices.
In such a situation a calendar user would like to be able to
"dismiss" the alarm on one device and have it dismissed on the others
too.
Also, with recurring events that have alarms, it is important to know
when the last alarm in the recurring set was acknowledged, so that
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the client can determine whether past alarms have been missed.
To address these needs, this specification adds an "ACKNOWLEDGED"
property to "VALARM" components to indicate when the alarm was last
sent or acknowledged. This is defined by the syntax below.
alarmprop /= *(
; the following is OPTIONAL,
; but MUST NOT occur more than once
acknowledged
)
7.1. Acknowledged Property
Property Name: ACKNOWLEDGED
Purpose: This property specifies the UTC date and time at which the
corresponding alarm was last sent or acknowledged.
Value Type: DATE-TIME
Property Parameters: IANA and non-standard property parameters can
be specified on this property.
Conformance: This property can be specified within "VALARM" calendar
components.
Description: This property is used to specify when an alarm was last
sent or acknowledged. This allows clients to determine when a
pending alarm has been acknowledged by a calendar user so that any
alerts can be dismissed across multiple devices. It also allows
clients to track repeating alarms or alarms on recurring events or
to-dos to ensure that the right number of missed alarms can be
tracked.
Clients SHOULD set this property to the current date-time value in
UTC when a calendar user acknowledges a pending alarm. Certain
kinds of alarm may not provide feedback as to when the calendar
user sees them, for example email based alerts. For those kinds
of alarms, the client SHOULD set this property when the alarm is
triggered and the action successfully carried out.
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Format Definition: This property is defined by the following
notation:
acknowledged = "ACKNOWLEDGED" acknowledgedparam ":" datetime CRLF
acknowledgedparam = *(
; the following is OPTIONAL,
; and MAY occur more than once
(";" other-param)
)
Example: The following is an example of this property:
ACKNOWLEDGED:20090604T084500Z
7.2. Examples
TODO Example of VALARM components
8. Snoozing Alarms
Users often want to "snooze" an alarm. That process effectively
creates a new alarm to be triggered a set amount of time after the
original being "snoozed". To accomplish this, clients SHOULD create
a new "VALARM" component within the same component of the "VALARM"
that was triggered and is being "snoozed". The new "VALARM" MUST be
set to trigger at the user's chosen "snooze" interval after the
original alarm triggered. To accomplish that clients SHOULD use an
absolute "TRIGGER" property with a "DATE-TIME" value specified in
UTC. When the "snooze" alarm is triggered and dismissed the client
SHOULD remove it from its parent component. Alternatively, if the
"snooze" alarm is itself "snoozed", the client SHOULD remote the
original "snooze" alarm and create a new one, with the appropriate
trigger time set.
9. VALARM Proximity Trigger Property
VALARMs are currently triggered when a specific date-time is reached.
It is also desirable to be able to trigger alarms based on location,
e.g. when arriving at or departing from a particular location.
This specification adds the following properties to "VALARM"
components to indicate when an alarm can be triggered based on
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location.
"PROXIMITY" - indicates that a location based trigger is to be
used and which direction of motion is used for the trigger
"GEO-LOCATION" - used to indicate the actual location to trigger
off, specified using a geo: URI [RFC5870] which allows for two or
three co-ordinate values with an optional uncertainty
alarmprop /= *(
; the following is OPTIONAL,
; but MUST NOT occur more than once
proximity /
; the following is OPTIONAL,
; and MAY occur more than once, but only
; when a PROXIMITY property is also present
geolocation
)
9.1. Proximity Property
Property Name: PROXIMITY
Purpose: This property indicates that a location based trigger is
applied to an alarm.
Value Type: TEXT
Property Parameters: IANA and non-standard property parameters can
be specified on this property.
Conformance: This property can be specified within "VALARM" calendar
components.
Description: This property is used to indicate that an alarm has a
location-based trigger. Its value identifies the direction of
motion used to trigger the alarm. One or more location values are
set using "GEO-LOCATION" properties.
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When the property value is set to "ARRIVE", the alarm is triggered
when the calendar user agent arrives in the vicinity of any of the
specified locations. When set to "DEPART", the alarm is triggered
when the calendar user agent departs from the vicinity of any
specified locations.
The time-based "TRIGGER" property MUST also be present in the
"VALARM" calendar component and MUST be set to a positive duration
value (or zero duration). That value indicates a time delay to be
applied to the triggering of the alarm after the location trigger
is triggered. e.g., an alarm could be set to trigger 30 minutes
after arriving home.
Format Definition: This property is defined by the following
notation:
proximity = "PROXIMITY" proximityparam ":" proximityvalue CRLF
proximityparam = *(
; the following is OPTIONAL,
; and MAY occur more than once
(";" other-param)
)
proximityvalue = "ARRIVE" / "DEPART" / iana-token / x-name
Example: The following is an example of this property:
PROXIMITY:ARRIVE
9.2. Geo Location Property
Property Name: GEO-LOCATION
Purpose: This property specifies a geo: URI [RFC5870] value.
Value Type: URI
Property Parameters: IANA and non-standard property parameters can
be specified on this property.
Conformance: This property can be specified multiple times within
"VALARM" calendar components, but only when a "PROXIMITY" property
is also present.
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Description: This property is used to specify a precise geo-location
that location aware calendar user agents can use to trigger an
alarm. The location is set using a geo: URI [RFC5870] which can
include a level of uncertainty (e.g., it can specify the
"vicinity" of a specific location). Calendar user agents MAY
apply their own tolerance to the specified location based on their
current location value precision.
Format Definition: This property is defined by the following
notation:
geolocation = "GEO-LOCATION" geolocationparam ":" uri CRLF
geolocationparam = *(
; the following is OPTIONAL,
; and MAY occur more than once
(";" other-param)
)
Example: The following is an example of this property:
GEO-LOCATION:geo:40.443,-79.945;u=10
9.3. Examples
TODO Example of VALARM components
10. Default Alarms in CalDAV
Users often want to have a default alarm applied to new events that
they create or to new invitations that arrive on a CalDAV [RFC4791]
server. Since this behavior is expected to occur no matter which
client a user is using, or whether any client is even connected at
the time, it is beneficial if the server itself is responsible for
managing the creation of the default alarm.
This specification defines four new WebDAV properties that can be
used to specify different sets of default alarms. Clients can store
"VALARM" components in these properties to setup the defaults. When
a new event or todo is created on the server, the server will
automatically add the default, as appropriate. When a new event or
todo invitation is delivered to the calendar user, the server will
automatically add the default alarm, as appropriate.
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The four new WebDAV properties are:
CALDAV:default-alarm-vevent-datetime A default alarm applied to
"VEVENT" components whose "DTSTART" property value type is "DATE-
TIME"
CALDAV:default-alarm-vevent-date A default alarm applied to "VEVENT"
components whose "DTSTART" property value type is "DATE"
CALDAV:default-alarm-vtodo-datetime A default alarm applied to
"VTODO" components whose "DUE" or "DTSTART" property value type is
"DATE-TIME"
CALDAV:default-alarm-vtodo-date A default alarm applied to "VTODO"
components whose "DUE" or "DTSTART" property value type is "DATE",
or when neither of those properties is present
The WebDAV properties are defined on a calendar user's "calendar
home" collection, or on individual calendar collections. When events
or tasks are created in a calendar, the server will first inspect the
WebDAV properties on the calendar collection to see if the
appropriate property is present. If it is, the server will use the
value of that property to set the default in the new component. If
the property is not present on the calendar collection, the server
will determine whether the property is present on the calendar home
collection that contains the calendar collection. If present on the
calendar home, the property value there is used as the default.
The WebDAV property value MUST be one or more "VALARM" components or
the empty string. If an empty string is used, no default alarms are
applied. Note that these values contain just the "BEGIN:
VALARM...END:VALARM" data (i.e., syntactically the "alarmcext"
element).
If a "DESCRIPTION" property is present in the "VALARM" component, but
its value is empty, the server SHOULD insert the value from any
"SUMMARY" property of the component in which the default "VALARM" is
being added.
11. Security Considerations
TODO:talk about importance of stripping VALARMs from incoming iTIP.
Talk about VALARMs being used to "spam" - particularly nasty if the
server handles it.
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12. IANA Considerations
12.1. Property Registrations
This document defines the following new iCalendar properties to be
added to the registry defined in Section 8.2.3 of [RFC5545]:
+--------------+---------+----------------------+
| Property | Status | Reference |
+--------------+---------+----------------------+
| ALARM-AGENT | Current | RFCXXXX, Section 6.1 |
| ACKNOWLEDGED | Current | RFCXXXX, Section 7.1 |
| PROXIMITY | Current | RFCXXXX, Section 9.1 |
| GEO-LOCATION | Current | RFCXXXX, Section 9.2 |
+--------------+---------+----------------------+
12.2. Parameter Registrations
This document defines the following new iCalendar property parameters
to be added to the registry defined in Section 8.2.4 of [RFC5545]:
+--------------------+---------+----------------------+
| Property Parameter | Status | Reference |
+--------------------+---------+----------------------+
| ID | Current | RFCXXXX, Section 6.2 |
+--------------------+---------+----------------------+
12.3. Actions Registry
This document defines the following new iCalendar action to be added
to the registry defined in Section 8.3.10 of [RFC5545]:
+--------+---------+--------------------+
| Action | Status | Reference |
+--------+---------+--------------------+
| URI | Current | RFCXXXX, Section 5 |
+--------+---------+--------------------+
13. Acknowledgments
This specification came about via discussions at the Calendaring and
Scheduling Consortium. Also, thanks to the following for providing
feedback: Bernard Desruisseaux, Mike Douglass, Jeffrey Harris, and
Ciny Joy.
14. References
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14.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4791] Daboo, C., Desruisseaux, B., and L. Dusseault,
"Calendaring Extensions to WebDAV (CalDAV)", RFC 4791,
March 2007.
[RFC5545] Desruisseaux, B., "Internet Calendaring and Scheduling
Core Object Specification (iCalendar)", RFC 5545,
September 2009.
[RFC5870] Mayrhofer, A. and C. Spanring, "A Uniform Resource
Identifier for Geographic Locations ('geo' URI)",
RFC 5870, June 2010.
14.2. Informative References
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3860] Peterson, J., "Common Profile for Instant Messaging
(CPIM)", RFC 3860, August 2004.
[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
RFC 3966, December 2004.
Appendix A. Change History (To be removed by RFC Editor before
publication)
Changes in -02:
1. Updated to 5545 reference.
2. Clarified use of absolute trigger in UTC in snooze alarms
3. Snooze alarms should be removed when completed
4. Removed status and replaced last-triggered by acknowledged
property
5. Added location-based trigger
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6. IANA registry tables added
Changes in -01:
1. Removed DESCRIPTION as an allowed property in the URI alarm.
2. Added statement about what to do when ALARM-AGENT is not present.
3. Allow multiple ALARM-AGENT properties to be present.
4. Removed SNOOZE-UNTIL - snoozing now accomplished by creating a
new VALARM.
5. Remove VALARM by reference section.
6. Added more detail to CalDAV default alarms.
Author's Address
Cyrus Daboo
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
USA
Email: cyrus@daboo.name
URI: http://www.apple.com/
Daboo Expires November 4, 2011 [Page 18]
