]> Spherical Cow Group

226 3rd Street Troy NY 12180 USA mdouglass@sphericalcowgroup.com http://sphericalcowgroup.com

Applications icalendar properties This specification updates RFC5545 by introducing a number of new iCalendar properties and components which are of particular use for event publishers and in social networking. This specification also defines a new STRUCTURED-DATA property for iCalendar RFC5545 to allow for data that is directly pertinent to an event or task to be included with the calendar data.

The currently existing iCalendar standard lacks useful methods for referencing additional, external information relating to calendar components. Additionally there is no standard way to provide rich text descriptions or meta-data associated with the event. Current practice is to embed this information as links in the description or to add non-standard properties as defined in section 3.8.8.2. This document updates to define a number of properties and a component referencing such external information that can provide additional information about an iCalendar component. The intent is to allow interchange of such information between applications or systems (e.g., between clients, between client and server, and between servers). Formats such as vCard are likely to be most useful to the receivers of such events as they may be used in other applications - such as address books.

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 BCP 14 when, and only when, they appear in all capitals, as shown here.

When the word 'event' is used (perhaps with a capitalised 'E' we are referring to gatherings, formal or informal. For example a sports event, a party or a concert. Historically, calendar data and scheduling has been heavily biased towards meetings in a corporate environment. Some of the features defined in this document are to support a more informal, i.e. social, model. For example, we may want to record who is participating in a public event.

Previous extensions to the calendaring standards have been largely restricted to the addition of properties or parameters. This is partly because iCalendar libraries had trouble handling components nested deeper than those defined in . In a break with this 'tradition' this specification defines PARTICIPANT as a component rather than a property. This is a better match for the way and JSON handle such structures and allows richer definitions. It also allows for the addition of extra properties inside the component and resolves some of the problems of trying to add detailed information as a parameter. Many people or groups may participate in an event. The PARTICIPANT component provides such detailed information. Participants may act as attendees to the event (or derived events) or may just provide a reference - perhaps for mailing lists.

The properties defined here can all reference external meta-data which may be used by applications to provide further information to users. By providing type information as parameters, clients and servers are able to discover interesting references and make use of them, perhaps for indexing or the presenting of additional related information for the user. As always, clients should exercise caution in following references to external data. The LOCATION property provides only an unstructured single text value for specifying the location where an event (or task) will occur. This is inadequate for use cases where structured location information (e.g. address, region, country, postal code) is required or preferred, and limits widespread adoption of iCalendar in those settings. Using STRUCTURED-LOCATION, rich information about multiple locations can be communicated, for example, address, region, country, postal code as well as other information such as parking availability, nearby restaurants and the venue. Servers and clients can retrieve the objects when storing the event and use them to index by geographic location. When a calendar client receives a calendar component it can search the set of supplied properties looking for those of particular interest. The TYPE and FMTTYPE parameters, if supplied, can be used to help the selection. The PARTICIPANT component is designed to handle common use cases in event publication. It is generally important to provide information about the organizers of such events. Sponsors wish to be referenced in a prominent manner. In social calendaring it is often important to identify the active participants in the event, for example a school sports team, and the inactive participants, for example the parents. The PARTICIPANT component can also be used to provide useful extra data about an attendee. For example a LOCATION property inside the PARTICIPANT gives the actual location of a remote attendee. (But see the note about privacy.)

The main motivation for these properties has been event publication but there are opportunities for use elsewhere. The following use cases will describe some possible scenarios.

In putting together a concert there are many participants: piano tuner, performer, stage hands etc. In addition there are sponsors and various contacts to be provided. There will also be a number of related locations. A number of events can be created, all of which relate to the performance in different ways. There may be an iTip meeting request for the piano tuner who will arrive before the performance. Other members of staff may also receive meeting requests. An event can also be created for publication which will have a PARTICIPANT component for the pianist providing a reference to vCard information about the performer. This event would also hold information about parking, local subway stations and the venue itself. In addition, there may be sponsorship information for sponsors of the event and perhaps paid sponsorship properties essentially advertising local establishments.

These additions also provide opportunities for the travel industry. When booking a flight the PARTICIPANT component can be used to provide references to businesses at the airports and to car hire businesses at the destination. The embedded location information can guide the traveler at the airport or to their final destination. The contact information can provide detailed information about the booking agent, the airlines, car hire companies and the hotel.

For a meeting, the size of a room and the equipment needed depends to some extent on the number of attendees actually in the room. A meeting may have 10 attendees none of which are co-located. The current ATTENDEE property does not allow for the addition of such meta-data. The PARTICIPANT component allows attendees to specify their location.

The following changes to the syntax defined in iCalendar are made here. New elements are defined in subsequent sections.

This specification makes use of the LABEL parameter which is defined in

LOCTYPE To specify the type(s) of a location.

This parameter is defined by the following notation: loctypeparam = "LOCTYPE" "=" quoted-string *("," quoted-string)

This parameter MAY be specified on STRUCTURED-LOCATION and provides a way to differentiate multiple properties. For example, it allows event producers to provide location information for the venue and the parking. Multiple values may be used if the location has multiple purposes, for example a hotel and a restaurant. Values for this parameter are taken from the values defined in section 3. New location types SHOULD be registered in the manner laid down in section 5 of that specification.

RESTYPE To specify the type of resource.

This parameter is defined by the following notation: restypeparam = "RESTYPE" "=" restypevalue CRLF restypevalue = ("ROOM" / "PROJECTOR" / "REMOTE-CONFERENCE-AUDIO" / "REMOTE-CONFERENCE-VIDEO" / iana-token) ; Other IANA-registered ; values

This parameter MAY be specified on STRUCTURED-RESOURCE and provides a way to differentiate multiple properties. The registered values are described below. New resource types SHOULD be registered in the manner laid down in this specification. A room for the event/meeting. Projection equipment. Audio remote conferencing facilities. Video remote conferencing facilities.

ORDER To define ordering for the associated property.

This parameter is defined by the following notation: orderparam = "ORDER" "=" integer ;Must be greater than or equal to 1

The ORDER parameter is OPTIONAL and is used to indicate the relative ordering of the corresponding instance of a property. Its value MUST be an integer greater than or equal to 1 that specifies the order with 1 being the first in the ordering. When the parameter is absent, the default MUST be to interpret the property instance as being ordered last, that is, the property will appear after any other instances of the same property with any value of ORDER. When any ORDER parameters have the same value all the associated properties appear as a group within which there is no defined order. Note that the value of this parameter is to be interpreted only in relation to values assigned to other corresponding instances of the same property in the same entity. This parameter MUST NOT be applied to a property that does not allow multiple instances. The ORDER may be applied to the PARTICIPANT-TYPE property to indicate the relative importance of the participant, for example as a sponsor or a performer. For example, ORDER=1 could define the principal performer or soloist.

SCHEMA To specify the schema used for the content of a "STRUCTURED-DATA" property value.

This parameter is defined by the following notation:

This property parameter SHOULD be specified on "STRUCTURED-DATA" properties. When present it provides identifying information about the nature of the content of the corresponding "STRUCTURED-DATA" property value. This can be used to supplement the media type information provided by the "FMTTYPE" parameter on the corresponding property.

DERIVED To specify that the value of the associated property is derived from some other property value or values.

This parameter is defined by the following notation:

This property parameter MAY be specified on any property when the value is derived from some other property or properties. When present with a value of TRUE clients MUST NOT update the property. As an example, if a STYLED-DESCRIPTION property is present with FMTTYPE="application/rtf" then there may be an additional STYLED-DESCRIPTION property with FMTTYPE="text/html" and DERIVED=TRUE and a value created from the rtf value.

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PARTICIPANT-TYPE To specify the type of participant. The value type for this property is TEXT. The allowable values are defined below. Non-standard parameters can be specified on this property. This property MUST be specified once within a PARTICIPANT component. This property defines the type of participation in events or tasks. Participants can be individuals or organizations, for example a soccer team, the spectators, or the musicians.

This property is defined by the following notation: participanttype = "PARTICIPANT-TYPE" partvalueparam ":" partvalue CRLF partvalue = ("ACTIVE" / "INACTIVE" / "SPONSOR" / "CONTACT" / "BOOKING-CONTACT" / "EMERGENCY-CONTACT" / "PUBLICITY-CONTACT" / "PLANNER-CONTACT" / "PERFORMER" / "SPEAKER" / iana-token) ; Other IANA-registered ; values partvalueparam = *( ; the following is OPTIONAL ; and MAY occur more than once ; (";" other-param) )

The following is an example of this property: PARTICIPANT-TYPE:SPEAKER

The registered values for the PARTICIPANT-TYPE property have the meanings described here: A participant taking an active role - for example a team member. A participant taking an inactive role - for example an audience member. A sponsor of the event. The ORDER parameter may be used with this participant type to define the relative order of multiple sponsors. Contact information for the event. The ORDER parameter may be used with this participant type to define the relative order of multiple contacts. Contact information for reservations or payment Contact in case of emergency Contact for publicity Contact for the event planner or organizer A performer - for example the soloist or the accompanist. The ORDER parameter may be used with this participant type to define the relative order of multiple performers. For example, ORDER=1 could define the principal performer or soloist. Speaker at an event

CALENDAR-ADDRESS To specify the calendar address for a participant. CAL-ADDRESS IANA, non-standard, language, calendar user type, group or list membership, participation role, participation status, RSVP expectation, delegatee, delegator, sent by, common name, or directory entry reference property parameters can be specified on this property. Additionally the schedule agent and schedule status parameters as defined in may be specified. This property MAY be specified once within a PARTICIPANT component. This property provides a calendar user address for the participant. If there is an ATTENDEE property with the same value then the participant is schedulable. If there is a related ATTENDEE proeprty then all parameters must be applied in that property.

This property is defined by the following notation: calendaraddress = "CALENDAR-ADDRESS" caladdressparam ":" cal-address CRLF caladdressparam = *( ; ; The following are OPTIONAL, ; but MUST NOT occur more than once. ; (";" cutypeparam) / (";" memberparam) / (";" roleparam) / (";" partstatparam) / (";" rsvpparam) / (";" deltoparam) / (";" delfromparam) / (";" sentbyparam) / (";" cnparam) / (";" dirparam) / (";" languageparam) / (";" scheduleagentparam) / (";" schedulestatusparam) / ; ; The following is OPTIONAL, ; and MAY occur more than once. ; (";" other-param) ; )

STYLED-DESCRIPTION This property provides for one or more rich-text descriptions to replace that provided by the DESCRIPTION property. There is no default value type for this property. The value type can be set to URI or TEXT. Other text-based value types can be used when defined in the future. Clients MUST ignore any properties with value types they do not understand. IANA, non-standard, id, alternate text representation, format type, derived and language property parameters can be specified on this property. The property can be specified multiple times in the "VEVENT", "VTODO", "VJOURNAL", "VFREEBUSY", "PARTICIPANT", or "VALARM" calendar components. If it does appear more than once there MUST be exactly one instance of the property with no DERIVED parameter or DERIVED=FALSE. All others MUST have DERIVED=TRUE. Additionally, if there is one or more STYLED-DESCRIPTION property then the DESCRIPTION property should be either absent or have the parameter DERIVED=TRUE. This property supports rich-text descriptions, for example HTML. Event publishers typically wish to provide more and better formatted information about the event. This property is used in the "VEVENT" and "VTODO" to capture lengthy textual descriptions associated with the activity. This property is used in the "VJOURNAL" calendar component to capture one or more textual journal entries. This property is used in the "VALARM" calendar component to capture the display text for a DISPLAY category of alarm, and to capture the body text for an EMAIL category of alarm. In the PARTICIPANT component it provides a detailed description of the participant. VALUE=TEXT is used to provide rich-text inline as the property value. VALUE=URI is used to provide a link to rich-text content which is expected to be displayed inline as part of the event. In either case the DESCRIPTION property should be absent or contain a plain text rendering of the styled text. Applications MAY attempt to guess the media type of the resource via inspection of its content if and only if the media type of the resource is not given by the "FMTTYPE" parameter. If the media type remains unknown, calendar applications SHOULD treat it as type "text/html" and process the content as defined in Multiple STYLED-DESCRIPTION properties may be used to provide different formats or different language variants. However all but one MUST have DERIVED=TRUE.

This property is defined by the following notation: styleddescription = "STYLED-DESCRIPTION" styleddescparam ":" styleddescval CRLF styleddescparam = *( ; The following is REQUIRED, ; but MUST NOT occur more than once. ; (";" "VALUE" "=" ("URI" / "TEXT")) / ; ; The following are OPTIONAL, ; but MUST NOT occur more than once. ; (";" altrepparam) / (";" languageparam) / (";" fmttypeparam) / (";" derivedparam) / ; ; the following is OPTIONAL ; and MAY occur more than once ; (";" other-param) ) styleddescval = ( uri / text ) ;Value MUST match value type

The following is an example of this property. It points to an html description. STYLED-DESCRIPTION;VALUE=URI:http://example.org/desc001.html

STRUCTURED-LOCATION This property provides a typed reference to external information about the location of an event or optionally a plain text typed value. There is no default value type for this property. The value type can be set to URI or TEXT. IANA, non-standard, label, loctype, related or format type parameters can be specified on this property. The LABEL parameter is defined in This property MAY be specified zero or more times in any iCalendar component. There may be a number of locations associated with an event. This provides detailed information about these locations. When used in a component the value of this property provides information about the event venue or of related services such as parking, dining, stations etc.. When a LABEL parameter is supplied the language of the label SHOULD match that of the content and of the LANGUAGE parameter if present. This allows a location to define the start and/or end timezone of the associated component. If a location is specified with a RELATED parameter then the affected DTSTART or DTEND properties MUST be specified as floating DATE-TIME value. If the RELATED parameter is present with a value of START, then the "DTSTART" property MUST be present in the associated "VEVENT" or "VTODO" calendar component. For an event, if the RELATED parameter is present with a value of END, then the "DTEND" property or the "DTSTART" and "DURATION " properties MUST be present in the associated "VEVENT" calendar component. For a to-do with a RELATED value of END, then either the "DUE" property or the "DTSTART" and "DURATION " properties MUST be present in the associated "VTODO" calendar component. If there is a location specified with RELATED=START and no location is specified with RELATED=END then the event is assumed to start and end in the same timezone.

This property is defined by the following notation: strucloc = "STRUCTURED-LOCATION" struclocparam ":" struclocval CRLF struclocparam = *( ; The following is REQUIRED, ; but MUST NOT occur more than once. ; (";" "VALUE" "=" ("URI" / "TEXT")) / ; ; the following are OPTIONAL ; but MUST NOT occur more than once ; (";" fmttypeparam) / (";" labelparam) / (";" languageparam) / (";" trigrelparam) / (";" loctypeparam) / ; ; the following is OPTIONAL ; and MAY occur more than once ; (";" other-param) ) struclocval = ( uri / text ) ;Value MUST match value type

The following is an example of this property. It points to a venue. STRUCTURED-LOCATION;LABEL="The venue"; VALUE=URI: http://dir.example.com/venues/big-hall.vcf

STRUCTURED-RESOURCE This property provides a typed reference to external information about a resource or optionally a plain text typed value. Typically a resource is anything that might be required or used by a calendar entity and possibly has a directory entry. There is no default value type for this property. The value type can be set to URI or TEXT. IANA, non-standard, label, restype or format type parameters can be specified on this property. The LABEL parameter is defined in The property can be specified multiple times in the "VEVENT" or "VTODO" calendar components. When used in a component the value of this property provides information about resources used for the event such as rooms, projectors, conferencing capabilities. Such resources may be a room or a projector. This RESTYPE value registry provides a place in which resource types may be registered for use by scheduling services. When a LABEL parameter is supplied the language of the label must match that of the content and of the LANGUAGE parameter if present.

This property is defined by the following notation: strucres = "STRUCTURED-RESOURCE" strucresparam ":" strucresval CRLF strucresparam = *( ; The following is REQUIRED, ; but MUST NOT occur more than once. ; (";" "VALUE" "=" ("URI" / "TEXT")) / ; ; the following are OPTIONAL ; but MUST NOT occur more than once ; (";" fmttypeparam) / (";" labelparam) / (";" languageparam) / (";" restypeparam) / ; ; the following is OPTIONAL ; and MAY occur more than once ; (";" other-param) ) strucresval = ( uri / text ) ;Value MUST match value type

The following is an example of this property. It refers to a projector. STRUCTURED-RESOURCE;value=uri;restype="projector": http://dir.example.com/projectors/3d.vcf

STRUCTURED-DATA This property specifies ancillary data associated with the calendar component. TEXT, BINARY or URI IANA, non-standard, inline encoding, and value data type property parameters can be specified on this property. The format type and schema parameters can be specified on this property and are RECOMMENDED for text or inline binary encoded content information. This property can be specified multiple times in an iCalendar object. Typically it would be used in "VEVENT", "VTODO", or "VJOURNAL" calendar components. The existing properties in iCalendar cover key elements of events and tasks such as start time, end time, location, summary, etc. However, different types of events often have other specific "fields" that it is useful to include in the calendar data. For example, an event representing an airline flight could include the airline, flight number, departure and arrival airport codes, check-in and gate-closing times etc. As another example, a sporting event might contain information about the type of sport, the home and away teams, the league the teams are in, information about nearby parking, etc. This property is used to specify ancillary data in some structured format either directly (inline) as a "TEXT" or "BINARY" value, or as a link via a "URI" value. Rather than define new iCalendar properties for the variety of event types that might occur, it would be better to leverage existing schemas for such data. For example, schemas available at https://schema.org include different event types. By using standard schemas, interoperability can be improved between calendar clients and non-calendaring systems that wish to generate or process the data. This property allows the direct inclusion of ancillary data whose schema is defined elsewhere. This property also includes parameters to clearly identify the type of the schema being used so that clients can quickly and easily spot what is relevant within the calendar data and present that to users or process it within the calendaring system. iCalendar does support an "ATTACH" property which can be used to include documents or links to documents within the calendar data. However, that property does not allow data to be included as a "TEXT" value (a feature that "STRUCTURED-DATA" does allow), plus attachments are often treated as "opaque" data to be processed by some other system rather than the calendar client. Thus the existing "ATTACH" property is not sufficient to cover the specific needs of inclusion of schema data. Extending the "ATTACH" property to support a new value type would likely cause interoperability problems. Additionally some implementations manage attachments by stripping them out and replacing with a link to the resource. Thus a new property to support inclusion of schema data is warranted.

This property is defined by the following notation:

The following is an example of this property:

PARTICIPANT This component provides information about a participant in an event or task. This component can be specified multiple times in a "VEVENT", "VTODO", "VJOURNAL", or "VFREEBUSY" calendar component. This component provides information about a participant in a calendar component. A participant may be an attendee in a scheduling sense and the ATTENDEE property may be specified in addition. Participants can be individuals or organizations, for example a soccer team, the spectators, or the musicians. STRUCTURED-DATA properties if present may refer to external definitions of the participant - such as a vCard. The CALENDAR-ADDRESS property if present will provide a cal-address. If an ATTENDEE property has the same value the participant is considered schedulable. The PARTICIPANT component can be used to contain additional meta-data related to the attendee.

This component is defined by the following notation: participantc = "BEGIN" ":" "PARTICIPANT" CRLF partprop "END" ":" "PARTICIPANT" CRLF partprop = *( ; ; The following are REQUIRED, ; but MUST NOT occur more than once. ; participanttype / uid / ; ; The following are OPTIONAL, ; but MUST NOT occur more than once. ; created / description / dtstamp / geo / last-mod / priority / seq / status / calendaraddress / summary / url / ; ; The following are OPTIONAL, ; and MAY occur more than once. ; attach / categories / comment / contact / location / rstatus / related / resources / strucloc / strucres / styleddescription / sdataprop / iana-prop ; )

When the PRIORITY is supplied it defines the ordering of PARTICIPANT components with the same value for the TYPE parameter. When a LOCATION is supplied it provides information about the location of a participant at a given time or times. This may represent an unacceptable privacy risk for some participants. User agents MUST NOT broadcast this information without the participant's express permission. For further comments see

The following is an example of this component. It contains a STRUCTURED-DATA property which points to a vCard providing information about the event participant. BEGIN:PARTICIPANT PARTICIPANT-TYPE:PERFORMER STRUCTURED-DATA;VALUE=URI:http://dir.example.com/vcard/aviolinist.vcf END:PARTICIPANT

The following is an example for the primary contact. BEGIN: PARTICIPANT STRUCTURED-DATA;VALUE=URI; http://dir.example.com/vcard/contacts/contact1.vcf PARTICIPANT-TYPE:CONTACT DESCRIPTION:A contact END:PARTICIPANT

A PARTICIPANT component may represent someone or something that needs to be scheduled as defined for ATTENDEE in and . The PARTICIPANT component may also represent someone or something that is NOT to receive scheduling messages. For backwards compatibility wuth existing clients and servers when used to schedule events and tasks the ATTENDEE property MUST be used to specify the sheduling parameters as defined for that property. For other, future uses the CALENDAR-ADDRESS property MUST be used to specify those parameters. A PARTICIPANT component is defined to be schedulable if It contains a CALENDAR-ADDRESS property That property value is the same as the value for an ATTENDEE property. If both of these conditions apply then the participant defined by the value of the URL property will take part in scheduling operations as defined in . An appropriate use for the PARTICIPANT component in scheduling would be to store SEQUENCE and DTSTAMP properties associated with replies from each ATTENDEE. A LOCATION property within the PARTICIPANT component might allow better selection of meeting times when participants are in different timezones.

The following are some examples of the use of the properties defined in this specification. They include additional properties defined in which includes IMAGE.

The following is an example of a VEVENT describing a concert. It includes location information for the venue itself as well as references to parking and restaurants. BEGIN:VEVENT CREATED:20200215T145739Z DESCRIPTION: Piano Sonata No 3\n Piano Sonata No 30 DTSTAMP:20200215T145739Z DTSTART;TZID=America/New_York:20200315T150000Z DTEND;TZID=America/New_York:20200315T163000Z LAST-MODIFIED:20200216T145739Z SUMMARY:Beethoven Piano Sonatas UID:123456 STRUCTURED-LOCATION;LABEL="The venue";VALUE=URI: http://dir.example.com/venues/big-hall.vcf STRUCTURED-LOCATION;LABEL="Parking for the venue";VALUE=URI: http://dir.example.com/venues/parking.vcf IMAGE;VALUE=URI;DISPLAY=BADGE;FMTTYPE=image/png:h ttp://example.com/images/concert.png BEGIN:PARTICIPANT PARTICIPANT-TYPE:SPONSOR UID:dG9tQGZvb2Jhci5xlLmNvbQ STRUCTURED-DATA;VALUE=URI:http://example.com/sponsor.vcf END:PARTICIPANT BEGIN:PARTICIPANT PARTICIPANT-TYPE:PERFORMER: UID:em9lQGZvb2GFtcGxlLmNvbQ STRUCTURED-DATA;VALUE=URI:http://www.example.com/people/johndoe.vcf END:PARTICIPANT END:VEVENT

The following is an example of a VEVENT describing a meeting. One of the attendees is a remote participant. BEGIN:VEVENT CREATED:20200215T145739Z DTSTAMP:20200215T145739Z DTSTART;TZID=America/New_York:20200315T150000Z DTEND;TZID=America/New_York:20200315T163000Z LAST-MODIFIED:20200216T145739Z SUMMARY:Conference planning UID:123456 ORGANIZER:mailto:a@example.com ATTENDEE;PARTSTAT=ACCEPTED;CN=A:mailto:a@example.com ATTENDEE;RSVP=TRUE;CN=B:mailto:b@example.com BEGIN:PARTICIPANT PARTICIPANT-TYPE:ACTIVE: UID:v39lQGZvb2GFtcGxlLmNvbQ STRUCTURED-DATA;VALUE=URI:http://www.example.com/people/b.vcf LOCATION:At home END:PARTICIPANT END:VEVENT

This specification extends and makes further use of possibly linked data. While calendar data is not unique in this regard it is worth reminding implementors of some of the dangers and safeguards.

See for a discussion of the security considerations relating to URIs. Fetching remote resources carries inherent risks. Connections must only be allowed on well known ports, using allowed protocols (generally just HTTP/HTTPS on their default ports). The URL must be resolved externally and not allowed to access internal resources. Connecting to an external source reveals IP (and therefore generally location) information. A maliciously constructed iCalendar object may contain a very large number of URIs. In the case of published calendars with a large number of subscribers, such objects could be widely distributed. Implementations should be careful to limit the automatic fetching of linked resources to reduce the risk of this being an amplification vector for a denial-of-service attack.

For the "STRUCTURED-DATA" property, servers need to be aware that a client could attack underlying storage by sending extremely large values and could attack processing time by uploading a recurring event with a large number of overrides and then repeatedly adding, updating, and deleting structured data. Malicious content could be introduced into the calendar server by way of the "STRUCTURED-DATA" property, and propagated to many end users via scheduling. Servers SHOULD check this property for malicious or inappropriate content. Upon detecting such content, servers SHOULD remove the property,

When processing HTML content, applications need to be aware of the many security and privacy issues, as described in the IANA considerations section of

Properties with a "URI" value type can expose their users to privacy leaks as any network access of the URI data can be tracked. Clients SHOULD NOT automatically download data referenced by the URI without explicit instruction from users. To help alleviate some of the concerns protocols and services could provide proxy services for downloading referenced data.

The addition of location information to the new participant component provides information about the location of participants at a given time. This information MUST NOT be distributed to other participants without that participants express permission. The same may be true of other information contained in the participant component. In general, revealing only as much as is absolutely necessary should be the approach For example, there may be some privacy considerations relating to the ORDER parameter, as it provides an indication of the organizer's perception of the relative importance of other participants.

This document defines the following new iCalendar properties to be added to the registry defined in Section 8.2.3 of : Property Status Reference CALENDAR-ADDRESS Current RFCXXXX, PARTICIPANT-TYPE Current RFCXXXX, STRUCTURED-DATA Current RFCXXXX, STYLED-DESCRIPTION Current RFCXXXX, STRUCTURED-LOCATION Current RFCXXXX, STRUCTURED-RESOURCE Current RFCXXXX,

This document defines the following new iCalendar property parameters to be added to the registry defined in Section 8.2.4 of : Property Parameter Status Reference LOCTYPE Current RFCXXXX, ORDER Current RFCXXXX, RESTYPE Current RFCXXXX, SCHEMA Current RFCXXXX,

This document defines the following new iCalendar components to be added to the registry defined in Section 8.3.1 of : Component Status Reference PARTICIPANT Current RFCXXXX,

This section defines new registration tables for PARTICIPANT-TYPE and RESTYPE values. These tables are updated using the same approaches laid down in Section 8.2.1 of

The following table has been used to initialize the participant types registry. Participant Type Status Reference ACTIVE Current RFCXXXX, INACTIVE Current RFCXXXX, SPONSOR Current RFCXXXX, CONTACT Current RFCXXXX, BOOKING-CONTACT Current RFCXXXX, EMERGENCY-CONTACT Current RFCXXXX, PUBLICITY-CONTACT Current RFCXXXX, PLANNER-CONTACT Current RFCXXXX, PERFORMER Current RFCXXXX, SPEAKER Current RFCXXXX,

The following table has been used to initialize the resource types registry. Resource Type Status Reference PROJECTOR Current RFCXXXX, ROOM Current RFCXXXX, REMOTE-CONFERENCE-AUDIO Current RFCXXXX, REMOTE-CONFERENCE-VIDEO Current RFCXXXX,

The author would like to thank Chuck Norris of eventful.com for his work which led to the development of this RFC. The author would also like to thank the members of CalConnect, The Calendaring and Scheduling Consortium, the Event Publication technical committee and the following individuals for contributing their ideas and support: Cyrus Daboo, John Haug, Dan Mendell, Ken Murchison, Scott Otis.

&RFC2119; &RFC2426; &RFC3986; &RFC4589; &RFC5545; &RFC5546; &RFC6638; &RFC7986; &RFC8174; &RFC8259; &W3C.REC-html51-20171003; &W3C.REC-xml-20081126;

None at the moment

To be deleted on publication calext-v16 2019-10-09 MD Make LOCTYPE multi-valued. Add all ATTENDEE scheduling parameters to CALENDAR-ADDRESS. calext-v15 2019-10-08 MD Address various DICUSS points. calext-v14 2019-06-11 MD Definition of event and social calendaring. Remove redefinition of SOURCE - use STRUCTURED-DATA. calext-v13 2019-05-26 MD Respond to various issues. calext-v12 2019-02-28 MD Fix styled-description example. Respond to various AD issues. Some typos. calext-v11 2019-02-27 MD Add DERIVED parameter for styled-description, RELATED parameter for structured-location calext-v09 2018-08-30 MD Sorted out inconsistencies in refs to 5546 calext-v08 2018-07-06 MD Add some text for equal ORDER values Switched scheduleaddress to calendaraddress in participant abnf. Also added more properties Fixed PARTICIPANT abnf calext-v04 2017-10-11 MD Change SCHEDULE-ADDRESS to CALENDAR-ADDRESS Explicitly broaden scope of SOURCE Add initial registry for RESTYPE and move new tables into separate section. Fix PARTTYPE/PARTICIPANT-TYPE inconsistency calext-v03 2017-10-09 MD Mostly typographical and other minor changes calext-v02 2017-04-20 MD Add SCHEDULE-ADDRESS property PARTICIPANT becomes a component rather than a property. Turn many of the former parameters into properties. Use existing ATTENDEE property for scheduling. calext-v01 2017-02-18 MD Change ASSOCIATE back to PARTICIPANT PARTICIPANT becomes a component rather than a property. Turn many of the former parameters into properties. calext-v00 2016-08-?? MD Name changed - taken up by calext working group v06 2016-06-26 MD Fix up abnf change ref to ietf from daboo take out label spec - use Cyrus spec v05 2016-06-14 MD Remove GROUP and HASH. they can be dealt with elsewhere if desired Change ORDER to integer >= 1. Incorporate Structured-Data into this specification. v04 2014-02-01 MD Added updates attribute. Minor typos. Resubmitted mostly to refresh the draft. v03 2013-03-06 MD Replace PARTICIPANT with ASSOCIATE plus related changes. Added section showing modifications to components. Replace ID with GROUP and modify HASH. Replace TITLE param with LABEL. Fixed STYLED-DESCRIPTION in various ways, correct example. v02 2012-11-02 MD Collapse sections with description of properties and the use cases into a section with sub-sections. New section to describe relating properties. Remove idref and upgrade hash to have the reference No default value types on properties.. v01 2012-10-18 MD Many changes. SPONSOR and STRUCTURED-CONTACT are now in PARTICIPANT Add a STRUCTURED-RESOURCE property STYLED-DESCRIPTION to handle rich text Much more... 2011-01-07 Remove MEDIA - it's going in the Cyrus RFC Rename EXTENDED-... to STRUCTURED-... Add TYPE parameter to SPONSOR v00 2007-10-19 MD Initial version