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Internet Engineering Task Force (IETF) C. Daboo
Request for Comments: 7986 Apple Inc.
Updates: 5545 October 2016
Category: Standards Track
ISSN: 2070-1721
New Properties for iCalendar
Abstract
This document defines a set of new properties for iCalendar data and
extends the use of some existing properties to the entire iCalendar
object.
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 7841.
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/rfc7986.
Copyright Notice
Copyright (c) 2016 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.
Daboo Standards Track [Page 1]
RFC 7986 iCalendar Property Extensions October 2016
Table of Contents
1. Introduction ....................................................3
2. Conventions Used in This Document ...............................3
3. Backwards-Compatible Extension Properties .......................3
4. Modifications to Calendar Components ............................4
5. Properties ......................................................5
5.1. NAME Property ..............................................5
5.2. DESCRIPTION Property .......................................6
5.3. UID Property ...............................................7
5.4. LAST-MODIFIED Property .....................................8
5.5. URL Property ...............................................8
5.6. CATEGORIES Property ........................................8
5.7. REFRESH-INTERVAL Property ..................................9
5.8. SOURCE Property ...........................................10
5.9. COLOR Property ............................................10
5.10. IMAGE Property ...........................................11
5.11. CONFERENCE Property ......................................13
6. Property Parameters ............................................14
6.1. DISPLAY Property Parameter ................................14
6.2. EMAIL Property Parameter ..................................15
6.3. FEATURE Property Parameter ................................16
6.4. LABEL Property Parameter ..................................17
7. Security Considerations ........................................18
8. Privacy Considerations .........................................18
9. IANA Considerations ............................................19
9.1. Property Registrations ....................................19
9.2. Parameter Registrations ...................................20
9.3. Property Parameter Value Registries .......................20
10. References ....................................................21
10.1. Normative References .....................................21
10.2. Informative References ...................................22
Acknowledgments ...................................................23
Author's Address ..................................................23
Daboo Standards Track [Page 2]
RFC 7986 iCalendar Property Extensions October 2016
1. Introduction
The iCalendar [RFC5545] data format is used to represent calendar
data and is used with the iCalendar Transport-Independent
Interoperability Protocol (iTIP) [RFC5546] to handle scheduling
operations between calendar users. iCalendar is in widespread use,
and in accordance with provisions in that specification, extension
elements have been added by various vendors to the data format in
order to support and enhance capabilities. This specification
collects a number of these ad hoc extensions and uses the new IANA
registry capability defined in [RFC5545] to register standard
variants with clearly defined definitions and semantics. In
addition, some new elements are introduced for features that vendors
have recently been requesting.
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].
The notation used in this memo is the ABNF notation of [RFC5234] as
used by iCalendar [RFC5545]. Any syntax elements shown below that
are not explicitly defined in this specification come from iCalendar
[RFC5545].
3. Backwards-Compatible Extension Properties
iCalendar defines properties that can have different value types
indicated by a "VALUE" parameter. The definition of a property
specifies a "default" value type that is assumed to be used when no
"VALUE" parameter is present. However, this poses a problem to the
iCalendar parser/generator software that does not know about the
default values for new properties. For example, if a new property
"FOO" were defined with a default value type of URI and a URI value
with a comma was used, an iCalendar generator not aware of this fact
would likely treat the property value as "TEXT" and apply backslash
escaping to the comma in the value, effectively making it an invalid
URI value.
To avoid this problem, this specification recommends that all
properties not defined in [RFC5545] always include a "VALUE"
parameter if the type is other than "TEXT". That is, in the example
above, the "FOO" property would have a "VALUE=URI" parameter. This
allows iCalendar parser/generator software to track the correct types
of unknown properties.
Daboo Standards Track [Page 3]
RFC 7986 iCalendar Property Extensions October 2016
New properties defined in this specification use the term "no
default" in the "Value Type" definition to indicate that the "VALUE"
parameter has to be included.
4. Modifications to Calendar Components
This section details changes to the syntax defined in iCalendar
[RFC5545]. New elements are defined in subsequent sections.
calprops =/ *(
;
; The following are OPTIONAL,
; but MUST NOT occur more than once.
;
uid / last-mod / url /
refresh / source / color
;
; The following are OPTIONAL,
; and MAY occur more than once.
;
name / description / categories /
image
;
)
eventprop =/ *(
;
; The following are OPTIONAL,
; but MUST NOT occur more than once.
;
color /
;
; The following are OPTIONAL,
; and MAY occur more than once.
;
conference / image
;
)
todoprop =/ *(
;
; The following are OPTIONAL,
; but MUST NOT occur more than once.
;
color /
;
; The following are OPTIONAL,
; and MAY occur more than once.
Daboo Standards Track [Page 4]
RFC 7986 iCalendar Property Extensions October 2016
;
conference / image
;
)
jourprop =/ *(
;
; The following are OPTIONAL,
; but MUST NOT occur more than once.
;
color /
;
; The following are OPTIONAL,
; and MAY occur more than once.
;
image
;
)
5. Properties
5.1. NAME Property
Property Name: NAME
Purpose: This property specifies the name of the calendar.
Value Type: TEXT
Property Parameters: IANA, non-standard, alternate text
representation, and language property parameters can be specified
on this property.
Conformance: This property can be specified multiple times in an
iCalendar object. However, each property MUST represent the name
of the calendar in a different language.
Description: This property is used to specify a name of the
iCalendar object that can be used by calendar user agents when
presenting the calendar data to a user. Whilst a calendar only
has a single name, multiple language variants can be specified by
including this property multiple times with different "LANGUAGE"
parameter values on each.
Daboo Standards Track [Page 5]
RFC 7986 iCalendar Property Extensions October 2016
Format Definition: This property is defined by the following
notation:
name = "NAME" nameparam ":" text CRLF
nameparam = *(
;
; The following are OPTIONAL,
; but MUST NOT occur more than once.
;
(";" altrepparam) / (";" languageparam) /
;
; The following is OPTIONAL,
; and MAY occur more than once.
;
(";" other-param)
;
)
Example: The following is an example of this property:
NAME:Company Vacation Days
5.2. DESCRIPTION Property
This specification modifies the definition of the "DESCRIPTION"
property to allow it to be defined in an iCalendar object. The
following additions are made to the definition of this property,
originally specified in Section 3.8.1.5 of [RFC5545].
Purpose: This property specifies the description of the calendar.
Conformance: This property can be specified multiple times in an
iCalendar object. However, each property MUST represent the
description of the calendar in a different language.
Description: This property is used to specify a lengthy textual
description of the iCalendar object that can be used by calendar
user agents when describing the nature of the calendar data to a
user. Whilst a calendar only has a single description, multiple
language variants can be specified by including this property
multiple times with different "LANGUAGE" parameter values on each.
Daboo Standards Track [Page 6]
RFC 7986 iCalendar Property Extensions October 2016
5.3. UID Property
This specification modifies the definition of the "UID" property to
allow it to be defined in an iCalendar object. The following
additions are made to the definition of this property, originally
specified in Section 3.8.4.7 of [RFC5545].
Purpose: This property specifies the persistent, globally unique
identifier for the iCalendar object. This can be used, for
example, to identify duplicate calendar streams that a client may
have been given access to. It can be used in conjunction with the
"LAST-MODIFIED" property also specified on the "VCALENDAR" object
to identify the most recent version of a calendar.
Conformance: This property can be specified once in an iCalendar
object.
The description of the "UID" property in [RFC5545] contains some
recommendations on how the value can be constructed. In particular,
it suggests use of host names, IP addresses, and domain names to
construct the value. However, this is no longer considered good
practice, particularly from a security and privacy standpoint, since
use of such values can leak key information about a calendar user or
their client and network environment. This specification updates
[RFC5545] by stating that "UID" values MUST NOT include any data that
might identify a user, host, domain, or any other security- or
privacy-sensitive information. It is RECOMMENDED that calendar user
agents now generate "UID" values that are hex-encoded random
Universally Unique Identifier (UUID) values as defined in
Sections 4.4 and 4.5 of [RFC4122].
The following is an example of such a property value:
UID:5FC53010-1267-4F8E-BC28-1D7AE55A7C99
Additionally, if calendar user agents choose to use other forms of
opaque identifiers for the "UID" value, they MUST have a length less
than 255 octets and MUST conform to the "iana-token" ABNF syntax
defined in Section 3.1 of [RFC5545].
Daboo Standards Track [Page 7]
RFC 7986 iCalendar Property Extensions October 2016
5.4. LAST-MODIFIED Property
This specification modifies the definition of the "LAST-MODIFIED"
property to allow it to be defined in an iCalendar object. The
following additions are made to the definition of this property,
originally specified in Section 3.8.7.3 of [RFC5545].
Purpose: This property specifies the date and time that the
information associated with the calendar was last revised.
Conformance: This property can be specified once in an iCalendar
object.
5.5. URL Property
This specification modifies the definition of the "URL" property to
allow it to be defined in an iCalendar object. The following
additions are made to the definition of this property, originally
specified in Section 3.8.4.6 of [RFC5545].
Purpose: This property may be used to convey a location where a more
dynamic rendition of the calendar information can be found.
Conformance: This property can be specified once in an iCalendar
object.
5.6. CATEGORIES Property
This specification modifies the definition of the "CATEGORIES"
property to allow it to be defined in an iCalendar object. The
following additions are made to the definition of this property,
originally specified in Section 3.8.1.2 of [RFC5545].
Purpose: This property defines the categories for an entire
calendar.
Conformance: This property can be specified multiple times in an
iCalendar object.
Description: When multiple properties are present, the set of
categories that apply to the iCalendar object are the union of all
the categories listed in each property value.
Daboo Standards Track [Page 8]
RFC 7986 iCalendar Property Extensions October 2016
5.7. REFRESH-INTERVAL Property
Property Name: REFRESH-INTERVAL
Purpose: This property specifies a suggested minimum interval for
polling for changes of the calendar data from the original source
of that data.
Value Type: DURATION -- no default
Property Parameters: IANA and non-standard property parameters can
be specified on this property.
Conformance: This property can be specified once in an iCalendar
object.
Description: This property specifies a positive duration that gives
a suggested minimum polling interval for checking for updates to
the calendar data. The value of this property SHOULD be used by
calendar user agents to limit the polling interval for calendar
data updates to the minimum interval specified.
Format Definition: This property is defined by the following
notation:
refresh = "REFRESH-INTERVAL" refreshparam
":" dur-value CRLF
;consisting of a positive duration of time.
refreshparam = *(
;
; The following is REQUIRED,
; but MUST NOT occur more than once.
;
(";" "VALUE" "=" "DURATION") /
;
; The following is OPTIONAL,
; and MAY occur more than once.
;
(";" other-param)
;
)
Example: The following is an example of this property:
REFRESH-INTERVAL;VALUE=DURATION:P1W
Daboo Standards Track [Page 9]
RFC 7986 iCalendar Property Extensions October 2016
5.8. SOURCE Property
Property Name: SOURCE
Purpose: This property identifies a URI where calendar data can be
refreshed from.
Value Type: URI -- no default
Property Parameters: IANA and non-standard property parameters can
be specified on this property.
Conformance: This property can be specified once in an iCalendar
object.
Description: This property identifies a location where a client can
retrieve updated data for the calendar. Clients SHOULD honor any
specified "REFRESH-INTERVAL" value when periodically retrieving
data. Note that this property differs from the "URL" property in
that "URL" is meant to provide an alternative representation of
the calendar data rather than the original location of the data.
Format Definition: This property is defined by the following
notation:
source = "SOURCE" sourceparam ":" uri CRLF
sourceparam = *(";" other-param)
Example: The following is an example of this property:
SOURCE;VALUE=URI:https://example.com/holidays.ics
5.9. COLOR Property
Property Name: COLOR
Purpose: This property specifies a color used for displaying the
calendar, event, todo, or journal data.
Value Type: TEXT
Property Parameters: IANA and non-standard property parameters can
be specified on this property.
Conformance: This property can be specified once in an iCalendar
object or in "VEVENT", "VTODO", or "VJOURNAL" calendar components.
Daboo Standards Track [Page 10]
RFC 7986 iCalendar Property Extensions October 2016
Description: This property specifies a color that clients MAY use
when presenting the relevant data to a user. Typically, this
would appear as the "background" color of events or tasks. The
value is a case-insensitive color name taken from the CSS3 set of
names, defined in Section 4.3 of [W3C.REC-css3-color-20110607].
Format Definition: This property is defined by the following
notation:
color = "COLOR" colorparam ":" text CRLF
; Value is CSS3 color name
colorparam = *(";" other-param)
Example: The following is an example of this property:
COLOR:turquoise
5.10. IMAGE Property
Property Name: IMAGE
Purpose: This property specifies an image associated with the
calendar or a calendar component.
Value Type: URI or BINARY -- no default. The value MUST be data
with a media type of "image" or refer to such data.
Property Parameters: IANA, non-standard, display, inline encoding,
and value data type property parameters can be specified on this
property. The format type parameter can be specified on this
property and is RECOMMENDED for inline binary-encoded content
information.
Conformance: This property can be specified multiple times in an
iCalendar object or in "VEVENT", "VTODO", or "VJOURNAL" calendar
components.
Description: This property specifies an image for an iCalendar
object or a calendar component via a URI or directly with inline
data that can be used by calendar user agents when presenting the
calendar data to a user. Multiple properties MAY be used to
specify alternative sets of images with, for example, varying
media subtypes, resolutions, or sizes. When multiple properties
are present, calendar user agents SHOULD display only one of them,
picking one that provides the most appropriate image quality, or
display none. The "DISPLAY" parameter is used to indicate the
intended display mode for the image. The "ALTREP" parameter,
Daboo Standards Track [Page 11]
RFC 7986 iCalendar Property Extensions October 2016
defined in [RFC5545], can be used to provide a "clickable" image
where the URI in the parameter value can be "launched" by a click
on the image in the calendar user agent.
Format Definition: This property is defined by the following
notation:
image = "IMAGE" imageparam
(
(
";" "VALUE" "=" "URI"
":" uri
) /
(
";" "ENCODING" "=" "BASE64"
";" "VALUE" "=" "BINARY"
":" binary
)
)
CRLF
imageparam = *(
;
; The following is OPTIONAL for a URI value,
; RECOMMENDED for a BINARY value,
; and MUST NOT occur more than once.
;
(";" fmttypeparam) /
;
; The following are OPTIONAL,
; and MUST NOT occur more than once.
;
(";" altrepparam) / (";" displayparam) /
;
; The following is OPTIONAL,
; and MAY occur more than once.
;
(";" other-param)
;
)
Example: The following is an example of this property:
IMAGE;VALUE=URI;DISPLAY=BADGE;FMTTYPE=image/png:h
ttp://example.com/images/party.png
Daboo Standards Track [Page 12]
RFC 7986 iCalendar Property Extensions October 2016
5.11. CONFERENCE Property
Property Name: CONFERENCE
Purpose: This property specifies information for accessing a
conferencing system.
Value Type: URI -- no default.
Property Parameters: IANA, non-standard, feature, and label property
parameters can be specified on this property.
Conformance: This property can be specified multiple times in a
"VEVENT" or "VTODO" calendar component.
Description: This property specifies information for accessing a
conferencing system for attendees of a meeting or task. This
might be for a telephone-based conference number dial-in with
access codes included (such as a tel: URI [RFC3966] or a sip: or
sips: URI [RFC3261]), for a web-based video chat (such as an http:
or https: URI [RFC7230]), or for an instant messaging group chat
room (such as an xmpp: URI [RFC5122]). If a specific URI for a
conferencing system is not available, a data: URI [RFC2397]
containing a text description can be used.
A conference system can be a bidirectional communication channel
or a uni-directional "broadcast feed".
The "FEATURE" property parameter is used to describe the key
capabilities of the conference system to allow a client to choose
the ones that give the required level of interaction from a set of
multiple properties.
The "LABEL" property parameter is used to convey additional
details on the use of the URI. For example, the URIs or access
codes for the moderator and attendee of a teleconference system
could be different, and the "LABEL" property parameter could be
used to "tag" each "CONFERENCE" property to indicate which is
which.
The "LANGUAGE" property parameter can be used to specify the
language used for text values used with this property (as per
Section 3.2.10 of [RFC5545]).
Daboo Standards Track [Page 13]
RFC 7986 iCalendar Property Extensions October 2016
Format Definition: This property is defined by the following
notation:
conference = "CONFERENCE" confparam ":" uri CRLF
confparam = *(
;
; The following is REQUIRED,
; but MUST NOT occur more than once.
;
(";" "VALUE" "=" "URI") /
;
; The following are OPTIONAL,
; and MUST NOT occur more than once.
;
(";" featureparam) / (";" labelparam) /
(";" languageparam ) /
;
; The following is OPTIONAL,
; and MAY occur more than once.
;
(";" other-param)
;
)
Example: The following are examples of this property:
CONFERENCE;VALUE=URI;FEATURE=PHONE,MODERATOR;
LABEL=Moderator dial-in:tel:+1-412-555-0123,,,654321
CONFERENCE;VALUE=URI;FEATURE=PHONE;
LABEL=Attendee dial-in:tel:+1-412-555-0123,,,555123
CONFERENCE;VALUE=URI;FEATURE=PHONE;
LABEL=Attendee dial-in:tel:+1-888-555-0456,,,555123
CONFERENCE;VALUE=URI;FEATURE=CHAT;
LABEL=Chat room:xmpp:chat-123@conference.example.com
CONFERENCE;VALUE=URI;FEATURE=AUDIO,VIDEO;
LABEL=Attendee dial-in:https://chat.example.com/audio?id=123456
6. Property Parameters
6.1. DISPLAY Property Parameter
Parameter Name: DISPLAY
Purpose: To specify different ways in which an image for a calendar
or component can be displayed.
Daboo Standards Track [Page 14]
RFC 7986 iCalendar Property Extensions October 2016
Format Definition: This property parameter is defined by the
following notation:
displayparam = "DISPLAY" "=" displayval *("," displayval)
displayval = ("BADGE" / ; image inline with the title of the
; event
"GRAPHIC" / ; a full image replacement for the event
; itself
"FULLSIZE" / ; an image that is used to enhance the
; event
"THUMBNAIL" / ; a smaller variant of "FULLSIZE" to be
; used when space for the image is
; constrained
x-name / ; Experimental type
iana-token) ; Other IANA-registered type
;
; Default is BADGE
Description: This property parameter MAY be specified on "IMAGE"
properties. In the absence of this parameter, the default value
"BADGE" MUST be used. The value determines how a client ought to
present an image supplied in iCalendar data to the user.
Values for this parameter are registered with IANA as per
Section 9.3.1. New values can be added to this registry following
the procedure outlined in Section 8.2.1 of [RFC5545].
Servers and clients MUST handle x-name and iana-token values they
don't recognize by not displaying any image at all.
Example:
IMAGE;VALUE=URI;DISPLAY=BADGE,THUMBNAIL;FMTTYPE=image/png:https://exa
mple.com/images/weather-cloudy.png
6.2. EMAIL Property Parameter
Parameter Name: EMAIL
Purpose: To specify an email address that is used to identify or
contact an organizer or attendee.
Format Definition: This property parameter is defined by the
following notation:
emailparam = "EMAIL" "=" param-value
Daboo Standards Track [Page 15]
RFC 7986 iCalendar Property Extensions October 2016
Description: This property parameter MAY be specified on "ORGANIZER"
or "ATTENDEE" properties. This property can be used in situations
where the calendar user address value of the "ORGANIZER" and
"ATTENDEE" properties is not likely to be an identifier that
recipients of scheduling messages could use to match the calendar
user with, for example, an address book entry. The value of this
property is an email address that can easily be matched by
recipients. Recipients can also use this value as an alternative
means of contacting the calendar user via email. If a recipient's
calendar user agent allows the recipient to save contact
information based on the "ORGANIZER" or "ATTENDEE" properties,
those calendar user agents SHOULD use any "EMAIL" property
parameter value for the email address of the contact over any
mailto: calendar user address specified as the value of the
property. Calendar user agents SHOULD NOT include an "EMAIL"
property parameter when its value matches the calendar user
address specified as the value of the property.
Example:
ATTENDEE;CN=Cyrus Daboo;EMAIL=cyrus@example.com:mailto:opaque-toke
n-1234@example.com
6.3. FEATURE Property Parameter
Parameter Name: FEATURE
Purpose: To specify a feature or features of a conference or
broadcast system.
Format Definition: This property parameter is defined by the
following notation:
featureparam = "FEATURE" "=" featuretext *("," featuretext)
featuretext = ("AUDIO" / ; Audio capability
"CHAT" / ; Chat or instant messaging
"FEED" / ; Blog or Atom feed
"MODERATOR" / ; Moderator dial-in code
"PHONE" / ; Phone conference
"SCREEN" / ; Screen sharing
"VIDEO" / ; Video capability
x-name / ; Experimental type
iana-token) ; Other IANA-registered type
Daboo Standards Track [Page 16]
RFC 7986 iCalendar Property Extensions October 2016
Description: This property parameter MAY be specified on the
"CONFERENCE" property. Multiple values can be specified. The
"MODERATOR" value is used to indicate that the property value is
specific to the owner/initiator of the conference and contains a
URI that "activates" the system (e.g., a "moderator" access code
for a phone conference system that is different from the "regular"
access code).
Example:
CONFERENCE;VALUE=URI;FEATURE=AUDIO:rtsp://audio.example.com/
event
CONFERENCE;VALUE=URI;FEATURE=AUDIO,VIDEO:https://video-chat.exam
ple.com/;group-id=1234
6.4. LABEL Property Parameter
Parameter Name: LABEL
Purpose: To provide a human-readable label.
Format Definition: This property parameter is defined by the
following notation:
labelparam = "LABEL" "=" param-value
Description: This property parameter MAY be specified on the
"CONFERENCE" property. It is anticipated that other extensions to
iCalendar will reuse this property parameter on new properties
that they define. As a result, clients MUST expect to find this
property parameter present on many different properties. It
provides a human-readable label that can be presented to calendar
users to allow them to discriminate between properties that might
be similar or provide additional information for properties that
are not self-describing. The "LANGUAGE" property parameter can be
used to specify the language of the text in the parameter value
(as per Section 3.2.10 of [RFC5545]).
Example:
CONFERENCE;VALUE=URI;FEATURE=VIDEO;
LABEL="Web video chat, access code=76543";
:https://video-chat.example.com/;group-id=1234
Daboo Standards Track [Page 17]
RFC 7986 iCalendar Property Extensions October 2016
7. Security Considerations
Several of the new properties or parameters defined by this
specification allow reference to "external" URIs. Care MUST be taken
when accessing data at external URIs as malicious content could be
present. Clients SHOULD ensure that suitable permission is granted
by calendar users before such URIs are dereferenced.
The "REFRESH-INTERVAL" property could be used by an attacker to make
a client carry out rapid requests to the server hosting the calendar
by specifying a very short duration (e.g., one second). This could
lead to resource consumption on the client or server and to denial-
of-service attacks against the server. Clients MUST ensure that they
throttle requests to the server to a reasonable rate. In most cases,
updating a public calendar once per day would suffice. If the
"REFRESH-INTERVAL" is any less than that, clients SHOULD warn the
calendar user and allow them to override it with a longer value.
The "CONFERENCE" property can include a "FEATURE" property parameter
with a "MODERATOR" value. In some cases, the access code used by the
owner/initiator of a conference might be private to an individual,
and clients and servers MUST ensure that such properties are not sent
to attendees of a scheduled component.
Both the "COLOR" and "IMAGE" properties are likely to be used by
calendar users to express their own personal view of the calendar
data. In addition, these properties could be used by attackers to
produce a confusing display in a calendar user agent. When such
properties are encountered in calendar data that has come from other
calendar users (e.g., via a scheduling message, "public" calendar
subscription, etc.), it is advisable for the client to give the
receiving calendar user the option to remove (or adjust) these
properties as the data is imported into their calendar system.
This specification changes the recommendations on how "UID" property
values are constructed to minimize leaking any information that might
be security sensitive.
Security considerations in [RFC5545] and [RFC5546] MUST also be
adhered to.
8. Privacy Considerations
Several of the new properties or parameters defined by this
specification allow reference to "external" URIs. Access to those
URIs could be tracked, leading to loss of privacy. Clients SHOULD
ensure that suitable permission is granted by calendar users before
such URIs are dereferenced. In particular, calendar publishers
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RFC 7986 iCalendar Property Extensions October 2016
wishing to help protect the privacy of their subscribers MUST use
HTTP with Transport Layer Security [RFC7230] ("https:" URIs instead
of "http:" URIs) for access to calendar data or ancillary data such
as images.
In general, for their own privacy protection, users have to rely on
the privacy policies of any conferencing system being accessed via
the "CONFERENCE" property. It is entirely possible for such systems
to uniquely identify and log the activity and participation (or lack
thereof) of calendar users in the conference. Calendar user agents
SHOULD track which conferencing systems are used and warn users the
first time a new one is about to be used. This is particularly
important if the client automatically "dials in" to the conference
when the event start time occurs.
By giving different calendar users different values for the "REFRESH-
INTERVAL" property, it is possible for a publisher of calendar data
to uniquely identify each refresh from each calendar users' clients
and thereby track user activity and IP address over time. To address
this, clients SHOULD add or subtract some random amount of time from
the published "REFRESH-INTERVAL" value when doing actual refreshes.
This specification changes the recommendations on how "UID" property
values are constructed to minimize leaking any information that might
be privacy sensitive.
Privacy considerations in [RFC5545] and [RFC5546] MUST also be
adhered to.
9. IANA Considerations
9.1. Property Registrations
This document defines the following new iCalendar properties. IANA
has registered the new properties in the "Properties" registry
defined in Section 8.3.2 of [RFC5545]. IANA has also added a
reference to this document where the properties originally defined in
RFC 5545 have been updated by this document.
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+------------------+---------+--------------------------------------+
| Property | Status | Reference |
+------------------+---------+--------------------------------------+
| NAME | Current | RFC 7986, Section 5.1 |
| DESCRIPTION | Current | RFC 5545, Section 3.8.1.5; RFC 7986, |
| | | Section 5.2 |
| UID | Current | RFC 5545, Section 3.8.4.7; RFC 7986, |
| | | Section 5.3 |
| LAST-MODIFIED | Current | RFC 5545, Section 3.8.7.3 RFC 7986, |
| | | Section 5.4 |
| URL | Current | RFC 5545, Section 3.8.4.6; RFC 7986, |
| | | Section 5.5 |
| CATEGORIES | Current | RFC 5545, Section 3.8.1.2; RFC 7986, |
| | | Section 5.6 |
| REFRESH-INTERVAL | Current | RFC 7986, Section 5.7 |
| SOURCE | Current | RFC 7986, Section 5.8 |
| COLOR | Current | RFC 7986, Section 5.9 |
| IMAGE | Current | RFC 7986, Section 5.10 |
| CONFERENCE | Current | RFC 7986, Section 5.11 |
+------------------+---------+--------------------------------------+
9.2. Parameter Registrations
This document defines the following new iCalendar property
parameters. IANA has registered these in the "Parameters" registry
defined in Section 8.3.3 of [RFC5545].
+--------------------+---------+-----------------------+
| Property Parameter | Status | Reference |
+--------------------+---------+-----------------------+
| DISPLAY | Current | RFC 7986, Section 6.1 |
| EMAIL | Current | RFC 7986, Section 6.2 |
| FEATURE | Current | RFC 7986, Section 6.3 |
| LABEL | Current | RFC 7986, Section 6.4 |
+--------------------+---------+-----------------------+
9.3. Property Parameter Value Registries
IANA has created two new registries for iCalendar elements: the
"Display Types" registry and the "Feature Types" registry.
Additional codes MAY be used, provided the process and template
described in Sections 8.2.1 and 8.2.6 of [RFC5545] are used to
register them.
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9.3.1. Display Types Registry
The following table has been used to initialize the "Display Types"
registry.
+--------------+---------+-----------------------+
| Display Type | Status | Reference |
+--------------+---------+-----------------------+
| BADGE | Current | RFC 7986, Section 6.1 |
| GRAPHIC | Current | RFC 7986, Section 6.1 |
| FULLSIZE | Current | RFC 7986, Section 6.1 |
| THUMBNAIL | Current | RFC 7986, Section 6.1 |
+--------------+---------+-----------------------+
9.3.2. Feature Types Registry
The following table has been used to initialize the "Feature Types"
registry.
+--------------+---------+-----------------------+
| Feature Type | Status | Reference |
+--------------+---------+-----------------------+
| AUDIO | Current | RFC 7986, Section 6.3 |
| CHAT | Current | RFC 7986, Section 6.3 |
| FEED | Current | RFC 7986, Section 6.3 |
| MODERATOR | Current | RFC 7986, Section 6.3 |
| PHONE | Current | RFC 7986, Section 6.3 |
| SCREEN | Current | RFC 7986, Section 6.3 |
| VIDEO | Current | RFC 7986, Section 6.3 |
+--------------+---------+-----------------------+
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<http://www.rfc-editor.org/info/rfc4122>.
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RFC 7986 iCalendar Property Extensions October 2016
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and
Scheduling Core Object Specification (iCalendar)",
RFC 5545, DOI 10.17487/RFC5545, September 2009,
<http://www.rfc-editor.org/info/rfc5545>.
[RFC5546] Daboo, C., Ed., "iCalendar Transport-Independent
Interoperability Protocol (iTIP)", RFC 5546,
DOI 10.17487/RFC5546, December 2009,
<http://www.rfc-editor.org/info/rfc5546>.
[W3C.REC-css3-color-20110607]
Celik, T., Lilley, C., and D. Baron, "CSS Color Module
Level 3", World Wide Web Consortium Recommendation
REC-css3-color-20110607, June 2011,
<https://www.w3.org/TR/2011/REC-css3-color-20110607>.
10.2. Informative References
[RFC2397] Masinter, L., "The "data" URL scheme", RFC 2397,
DOI 10.17487/RFC2397, August 1998,
<http://www.rfc-editor.org/info/rfc2397>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<http://www.rfc-editor.org/info/rfc3261>.
[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
RFC 3966, DOI 10.17487/RFC3966, December 2004,
<http://www.rfc-editor.org/info/rfc3966>.
[RFC5122] Saint-Andre, P., "Internationalized Resource Identifiers
(IRIs) and Uniform Resource Identifiers (URIs) for the
Extensible Messaging and Presence Protocol (XMPP)",
RFC 5122, DOI 10.17487/RFC5122, February 2008,
<http://www.rfc-editor.org/info/rfc5122>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
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Acknowledgments
Thanks to the following individuals for feedback: Bernard
Desruisseaux, Mike Douglass, Lucia Fedorova, Ken Murchison, Arnaud
Quillaud, and Dave Thewlis.
This specification came about via discussions at the Calendaring and
Scheduling Consortium.
Author's Address
Cyrus Daboo
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
United States of America
Email: cyrus@daboo.name
URI: http://www.apple.com/
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