Internet Engineering Task Force (IETF)                        N. Jenkins
Request for Comments: 8984                                   R. Stepanek
Category: Standards Track                                       Fastmail
ISSN: 2070-1721                                                July 2021


           JSCalendar: A JSON Representation of Calendar Data

Abstract

   This specification defines a data model and JSON representation of
   calendar data that can be used for storage and data exchange in a
   calendaring and scheduling environment.  It aims to be an alternative
   and, over time, successor to the widely deployed iCalendar data
   format.  It also aims to be unambiguous, extendable, and simple to
   process.  In contrast to the jCal format, which is also based on
   JSON, JSCalendar is not a direct mapping from iCalendar but defines
   the data model independently and expands semantics where appropriate.

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
   https://www.rfc-editor.org/info/rfc8984.

Copyright Notice

   Copyright (c) 2021 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
   (https://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.

Table of Contents

   1.  Introduction
     1.1.  Motivation and Relation to iCalendar and jCal
     1.2.  Notational Conventions
     1.3.  Type Signatures
     1.4.  Data Types
       1.4.1.  Id
       1.4.2.  Int
       1.4.3.  UnsignedInt
       1.4.4.  UTCDateTime
       1.4.5.  LocalDateTime
       1.4.6.  Duration
       1.4.7.  SignedDuration
       1.4.8.  TimeZoneId
       1.4.9.  PatchObject
       1.4.10. Relation
       1.4.11. Link
   2.  JSCalendar Objects
     2.1.  Event
     2.2.  Task
     2.3.  Group
   3.  Structure of JSCalendar Objects
     3.1.  Object Type
     3.2.  Normalization and Equivalence
     3.3.  Vendor-Specific Property Extensions, Values, and Types
   4.  Common JSCalendar Properties
     4.1.  Metadata Properties
       4.1.1.  @type
       4.1.2.  uid
       4.1.3.  relatedTo
       4.1.4.  prodId
       4.1.5.  created
       4.1.6.  updated
       4.1.7.  sequence
       4.1.8.  method
     4.2.  What and Where Properties
       4.2.1.  title
       4.2.2.  description
       4.2.3.  descriptionContentType
       4.2.4.  showWithoutTime
       4.2.5.  locations
       4.2.6.  virtualLocations
       4.2.7.  links
       4.2.8.  locale
       4.2.9.  keywords
       4.2.10. categories
       4.2.11. color
     4.3.  Recurrence Properties
       4.3.1.  recurrenceId
       4.3.2.  recurrenceIdTimeZone
       4.3.3.  recurrenceRules
       4.3.4.  excludedRecurrenceRules
       4.3.5.  recurrenceOverrides
       4.3.6.  excluded
     4.4.  Sharing and Scheduling Properties
       4.4.1.  priority
       4.4.2.  freeBusyStatus
       4.4.3.  privacy
       4.4.4.  replyTo
       4.4.5.  sentBy
       4.4.6.  participants
       4.4.7.  requestStatus
     4.5.  Alerts Properties
       4.5.1.  useDefaultAlerts
       4.5.2.  alerts
     4.6.  Multilingual Properties
       4.6.1.  localizations
     4.7.  Time Zone Properties
       4.7.1.  timeZone
       4.7.2.  timeZones
   5.  Type-Specific JSCalendar Properties
     5.1.  Event Properties
       5.1.1.  start
       5.1.2.  duration
       5.1.3.  status
     5.2.  Task Properties
       5.2.1.  due
       5.2.2.  start
       5.2.3.  estimatedDuration
       5.2.4.  percentComplete
       5.2.5.  progress
       5.2.6.  progressUpdated
     5.3.  Group Properties
       5.3.1.  entries
       5.3.2.  source
   6.  Examples
     6.1.  Simple Event
     6.2.  Simple Task
     6.3.  Simple Group
     6.4.  All-Day Event
     6.5.  Task with a Due Date
     6.6.  Event with End Time Zone
     6.7.  Floating-Time Event (with Recurrence)
     6.8.  Event with Multiple Locations and Localization
     6.9.  Recurring Event with Overrides
     6.10. Recurring Event with Participants
   7.  Security Considerations
     7.1.  Expanding Recurrences
     7.2.  JSON Parsing
     7.3.  URI Values
     7.4.  Spam
     7.5.  Duplication
     7.6.  Time Zones
   8.  IANA Considerations
     8.1.  Media Type Registration
     8.2.  Creation of the "JSCalendar Properties" Registry
       8.2.1.  Preliminary Community Review
       8.2.2.  Submit Request to IANA
       8.2.3.  Designated Expert Review
       8.2.4.  Change Procedures
       8.2.5.  "JSCalendar Properties" Registry Template
       8.2.6.  Initial Contents for the "JSCalendar Properties"
               Registry
     8.3.  Creation of the "JSCalendar Types" Registry
       8.3.1.  "JSCalendar Types" Registry Template
       8.3.2.  Initial Contents for the "JSCalendar Types" Registry
     8.4.  Creation of the "JSCalendar Enum Values" Registry
       8.4.1.  "JSCalendar Enum Values" Registry Property Template
       8.4.2.  "JSCalendar Enum Values" Registry Value Template
       8.4.3.  Initial Contents for the "JSCalendar Enum Values"
               Registry
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   This document defines a data model for calendar event and task
   objects, or groups of such objects, in electronic calendar
   applications and systems.  The format aims to be unambiguous,
   extendable, and simple to process.

   The key design considerations for this data model are as follows:

   *  The attributes of the calendar entry represented must be described
      as simple key-value pairs.  Simple events are simple to represent;
      complex events can be modeled accurately.

   *  Wherever possible, there should be only one way to express the
      desired semantics, reducing complexity.

   *  The data model should avoid ambiguities, which often lead to
      interoperability issues between implementations.

   *  The data model should be generally compatible with the iCalendar
      data format [RFC5545] [RFC7986] and extensions, but the
      specification should add new attributes where the iCalendar format
      currently lacks expressivity, and drop seldom-used, obsolete, or
      redundant properties.  This means translation with no loss of
      semantics should be easy with most common iCalendar files.

   *  Extensions, such as new properties and components, should not
      require updates to this document.

   The representation of this data model is defined in the Internet JSON
   (I-JSON) format [RFC7493], which is a strict subset of the JSON data
   interchange format [RFC8259].  Using JSON is mostly a pragmatic
   choice: its widespread use makes JSCalendar easier to adopt and the
   ready availability of production-ready JSON implementations
   eliminates a whole category of parser-related interoperability
   issues, which iCalendar has often suffered from.

1.1.  Motivation and Relation to iCalendar and jCal

   The iCalendar data format [RFC5545], a widely deployed interchange
   format for calendaring and scheduling data, has served calendaring
   vendors for a long time but contains some ambiguities and pitfalls
   that cannot be overcome without backward-incompatible changes.

   Sources of implementation errors include the following:

   *  iCalendar defines various formats for local times, UTC, and dates.

   *  iCalendar requires custom time zone definitions within a single
      calendar component.

   *  iCalendar's definition of recurrence rules is ambiguous and has
      resulted in differing interpretations, even between experienced
      calendar developers.

   *  The iCalendar format itself causes interoperability issues due to
      misuse of CRLF-terminated strings, line continuations, and subtle
      differences among iCalendar parsers.

   In recent years, many new products and services have appeared that
   wish to use a JSON representation of calendar data within their APIs.
   The JSON format for iCalendar data, jCal [RFC7265], is a direct
   mapping between iCalendar and JSON.  In its effort to represent full
   iCalendar semantics, it inherits all the same pitfalls and uses a
   complicated JSON structure.

   As a consequence, since the standardization of jCal, the majority of
   implementations and service providers either kept using iCalendar or
   came up with their own proprietary JSON representations, which are
   incompatible with each other and often suffer from common pitfalls,
   such as storing event start times in UTC (which become incorrect if
   the time zone's rules change in the future).  JSCalendar meets the
   demand for JSON-formatted calendar data that is free of such known
   problems and provides a standard representation as an alternative to
   the proprietary formats.

1.2.  Notational Conventions

   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 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The underlying format used for this specification is JSON.
   Consequently, the terms "object" and "array" as well as the four
   primitive types (strings, numbers, booleans, and null) are to be
   interpreted as described in Section 1 of [RFC8259].

   Some examples in this document contain "partial" JSON documents used
   for illustrative purposes.  In these examples, an ellipsis "..." is
   used to indicate a portion of the document that has been removed for
   compactness.

1.3.  Type Signatures

   Type signatures are given for all JSON values in this document.  The
   following conventions are used:

   "*":  The type is undefined (the value could be any type, although
      permitted values may be constrained by the context of this value).

   "String":  This is the JSON string type.

   "Number":  This is the JSON number type.

   "Boolean":  This is the JSON boolean type.

   "A[B]":  The keys are all of type "A" and the values are all of type
      "B" for a JSON object.

   "A[]":  There is an array of values of type "A"

   "A|B":  The value is either of type "A" or of type "B".

   Other types may also be given; their representations are defined
   elsewhere in this document.

1.4.  Data Types

   In addition to the standard JSON data types, the following data types
   are used in this specification:

1.4.1.  Id

   Where "Id" is given as a data type, it means a "String" of at least 1
   and a maximum of 255 octets in size, and it MUST only contain
   characters from the "URL and Filename Safe" base64url alphabet, as
   defined in Section 5 of [RFC4648], excluding the pad character ("=").
   This means the allowed characters are the ASCII alphanumeric
   characters ("A-Za-z0-9"), hyphen ("-"), and underscore ("_").

   In many places in JSCalendar, a JSON map is used where the map keys
   are of type Id and the map values are all the same type of object.
   This construction represents an unordered set of objects, with the
   added advantage that each entry has a name (the corresponding map
   key).  This allows for more concise patching of objects, and, when
   applicable, for the objects in question to be referenced from other
   objects within the JSCalendar object.

   Unless otherwise specified for a particular property, there are no
   uniqueness constraints on an Id value (other than, of course, the
   requirement that you cannot have two values with the same key within
   a single JSON map).  For example, two Event objects might use the
   same Ids in their respective "links" properties or, within the same
   Event object, the same Id could appear in the "participants" and
   "alerts" properties.  These situations do not imply any semantic
   connections among the objects.

1.4.2.  Int

   Where "Int" is given as a data type, it means an integer in the range
   -2^53+1 <= value <= 2^53-1, the safe range for integers stored in a
   floating-point double, represented as a JSON "Number".

1.4.3.  UnsignedInt

   Where "UnsignedInt" is given as a data type, it means an integer in
   the range 0 <= value <= 2^53-1, represented as a JSON "Number".

1.4.4.  UTCDateTime

   This is a string in the "date-time" [RFC3339] format, with the
   further restrictions that any letters MUST be in uppercase, and the
   time offset MUST be the character "Z".  Fractional second values MUST
   NOT be included unless non-zero and MUST NOT have trailing zeros, to
   ensure there is only a single representation for each date-time.

   For example, "2010-10-10T10:10:10.003Z" is conformant, but
   "2010-10-10T10:10:10.000Z" is invalid and is correctly encoded as
   "2010-10-10T10:10:10Z".

1.4.5.  LocalDateTime

   This is a date-time string with no time zone/offset information.  It
   is otherwise in the same format as UTCDateTime, including fractional
   seconds.  For example, "2006-01-02T15:04:05" and
   "2006-01-02T15:04:05.003" are both valid.  The time zone to associate
   with the LocalDateTime comes from the "timeZone" property of the
   JSCalendar object (see Section 4.7.1).  If no time zone is specified,
   the LocalDateTime is "floating".  Floating date-times are not tied to
   any specific time zone.  Instead, they occur in each time zone at the
   given wall-clock time (as opposed to the same instant point in time).

   A time zone may have a period of discontinuity, for example, a change
   from standard time to daylight savings time.  When converting local
   date-times that fall in the discontinuity to UTC, the offset before
   the transition MUST be used.

   For example, in the America/Los_Angeles time zone, the date-time
   2020-11-01T01:30:00 occurs twice: before the daylight savings time
   (DST) transition with a UTC offset of -07:00 and again after the
   transition with an offset of -08:00.  When converting to UTC, we
   therefore use the offset before the transition (-07:00), so it
   becomes 2020-11-01T08:30:00Z.

   Similarly, in the Australia/Melbourne time zone, the date-time
   2020-10-04T02:30:00 does not exist; the clocks are moved forward one
   hour for DST on that day at 02:00.  However, such a value may appear
   during calculations (see duration semantics in Section 1.4.6) or due
   to a change in time zone rules (so it was valid when the event was
   first created).  Again, it is interpreted as though the offset before
   the transition is in effect (+10:00); therefore, when converted to
   UTC, we get 2020-10-03T16:30:00Z.

1.4.6.  Duration

   Where Duration is given as a type, it means a length of time
   represented by a subset of the ISO 8601 duration format, as specified
   by the following ABNF [RFC5234]:

       dur-secfrac = "." 1*DIGIT
       dur-second  = 1*DIGIT [dur-secfrac] "S"
       dur-minute  = 1*DIGIT "M" [dur-second]
       dur-hour    = 1*DIGIT "H" [dur-minute]
       dur-time    = "T" (dur-hour / dur-minute / dur-second)
       dur-day     = 1*DIGIT "D"
       dur-week    = 1*DIGIT "W"
       dur-cal     = (dur-week [dur-day] / dur-day)

       duration    = "P" (dur-cal [dur-time] / dur-time)

   In addition, the duration MUST NOT include fractional second values
   unless the fraction is non-zero.  Fractional second values MUST NOT
   have trailing zeros to ensure there is only a single representation
   for each duration.

   A duration specifies an abstract number of weeks, days, hours,
   minutes, and/or seconds.  A duration specified using weeks or days
   does not always correspond to an exact multiple of 24 hours.  The
   number of hours/minutes/seconds may vary if it overlaps a period of
   discontinuity in the event's time zone, for example, a change from
   standard time to daylight savings time.  Leap seconds MUST NOT be
   considered when adding or subtracting a duration to/from a
   LocalDateTime.

   To add a duration to a LocalDateTime:

   1.  Add any week or day components of the duration to the date.  A
       week is always the same as seven days.

   2.  If a time zone applies to the LocalDateTime, convert it to a
       UTCDateTime following the semantics in Section 1.4.5.

   3.  Add any hour, minute, or second components of the duration (in
       absolute time).

   4.  Convert the resulting UTCDateTime back to a LocalDateTime in the
       time zone that applies.

   To subtract a duration from a LocalDateTime, the steps apply in
   reverse:

   1.  If a time zone applies to the LocalDateTime, convert it to UTC
       following the semantics in Section 1.4.5.

   2.  Subtract any hour, minute, or second components of the duration
       (in absolute time).

   3.  Convert the resulting UTCDateTime back to LocalDateTime in the
       time zone that applies.

   4.  Subtract any week or day components of the duration from the
       date.

   5.  If the resulting time does not exist on the date due to a
       discontinuity in the time zone, use the semantics in
       Section 1.4.5 to convert to UTC and back to get a valid
       LocalDateTime.

   These semantics match the iCalendar DURATION value type ([RFC5545],
   Section 3.3.6).

1.4.7.  SignedDuration

   A SignedDuration represents a length of time that may be positive or
   negative and is typically used to express the offset of a point in
   time relative to an associated time.  It is represented as a
   Duration, optionally preceded by a sign character.  It is specified
   by the following ABNF:

   signed-duration = ["+" / "-"] duration

   A negative sign indicates a point in time at or before the associated
   time; a positive or no sign indicates a time at or after the
   associated time.

1.4.8.  TimeZoneId

   Where "TimeZoneId" is given as a data type, it means a "String" that
   is either a time zone name in the IANA Time Zone Database [TZDB] or a
   custom time zone identifier defined in the "timeZones" property (see
   Section 4.7.2).

   Where an IANA time zone is specified, the zone rules of the
   respective zone records apply.  Custom time zones are interpreted as
   described in Section 4.7.2.

1.4.9.  PatchObject

   A PatchObject is of type "String[*]" and represents an unordered set
   of patches on a JSON object.  Each key is a path represented in a
   subset of the JSON Pointer format [RFC6901].  The paths have an
   implicit leading "/", so each key is prefixed with "/" before
   applying the JSON Pointer evaluation algorithm.

   A patch within a PatchObject is only valid if all of the following
   conditions apply:

   1.  The pointer MUST NOT reference inside an array (i.e., you MUST
       NOT insert/delete from an array; the array MUST be replaced in
       its entirety instead).

   2.  All parts prior to the last (i.e., the value after the final
       slash) MUST already exist on the object being patched.

   3.  There MUST NOT be two patches in the PatchObject where the
       pointer of one is the prefix of the pointer of the other, e.g.,
       "alerts/1/offset" and "alerts".

   4.  The value for the patch MUST be valid for the property being set
       (of the correct type and obeying any other applicable
       restrictions), or, if null, the property MUST be optional.

   The value associated with each pointer determines how to apply that
   patch:

   *  If null, remove the property from the patched object.  If the key
      is not present in the parent, this a no-op.

   *  If non-null, set the value given as the value for this property
      (this may be a replacement or addition to the object being
      patched).

   A PatchObject does not define its own "@type" property (see
   Section 4.1.1).  An "@type" property in a patch MUST be handled as
   any other patched property value.

   Implementations MUST reject a PatchObject in its entirety if any of
   its patches are invalid.  Implementations MUST NOT apply partial
   patches.

   The PatchObject format is used to significantly reduce file size and
   duplicated content when specifying variations to a common object,
   such as with recurring events or when translating the data into
   multiple languages.  It can also better preserve semantic intent if
   only the properties that should differ between the two objects are
   patched.  For example, if one person is not going to a particular
   instance of a regularly scheduled event, in iCalendar, you would have
   to duplicate the entire event in the override.  In JSCalendar, this
   is a small patch to show the difference.  As only this property is
   patched, if the location of the event is changed, the occurrence will
   automatically still inherit this.

1.4.10.  Relation

   A Relation object defines the relation to other objects, using a
   possibly empty set of relation types.  The object that defines this
   relation is the linking object, while the other object is the linked
   object.  A Relation object has the following properties:

   @type: "String" (mandatory)
      This specifies the type of this object.  This MUST be "Relation".

   relation: "String[Boolean]" (optional, default: empty Object)
      This describes how the linked object is related to the linking
      object.  The relation is defined as a set of relation types.  If
      empty, the relationship between the two objects is unspecified.

      Keys in the set MUST be one of the following values, specified in
      the property definition where the Relation object is used, a value
      registered in the IANA "JSCalendar Enum Values" registry, or a
      vendor-specific value (see Section 3.3):

      "first":  The linked object is the first in a series the linking
         object is part of.

      "next":  The linked object is next in a series the linking object
         is part of.

      "child":  The linked object is a subpart of the linking object.

      "parent":  The linking object is a subpart of the linked object.

      The value for each key in the map MUST be true.

1.4.11.  Link

   A Link object represents an external resource associated with the
   linking object.  It has the following properties:

   @type: "String" (mandatory)
      This specifies the type of this object.  This MUST be "Link".

   href: "String" (mandatory)
      This is a URI [RFC3986] from which the resource may be fetched.

      This MAY be a "data:" URL [RFC2397], but it is recommended that
      the file be hosted on a server to avoid embedding arbitrarily
      large data in JSCalendar object instances.

   cid: "String" (optional)
      This MUST be a valid "content-id" value according to the
      definition of Section 2 of [RFC2392].  The value MUST be unique
      within this Link object but has no meaning beyond that.  It MAY be
      different from the link id for this Link object.

   contentType: "String" (optional)
      This is the media type [RFC6838] of the resource, if known.

   size: "UnsignedInt" (optional)
      This is the size, in octets, of the resource when fully decoded
      (i.e., the number of octets in the file the user would download),
      if known.  Note that this is an informational estimate, and
      implementations must be prepared to handle the actual size being
      quite different when the resource is fetched.

   rel: "String" (optional)
      This identifies the relation of the linked resource to the object.
      If set, the value MUST be a relation type from the IANA "Link
      Relations" registry [LINKRELS], as established in [RFC8288].

   display: "String" (optional)
      This describes the intended purpose of a link to an image.  If
      set, the "rel" property MUST be set to "icon".  The value MUST be
      one of the following values, another value registered in the IANA
      "JSCalendar Enum Values" registry, or a vendor-specific value (see
      Section 3.3):

      "badge":  an image meant to be displayed alongside the title of
         the object

      "graphic":  a full image replacement for the object itself

      "fullsize":  an image that is used to enhance the object

      "thumbnail":  a smaller variant of "fullsize" to be used when
         space for the image is constrained

   title: "String" (optional)
      This is a human-readable, plain-text description of the resource.

2.  JSCalendar Objects

   This section describes the calendar object types specified by
   JSCalendar.

2.1.  Event

   Media type: "application/jscalendar+json;type=event"

   An Event represents a scheduled amount of time on a calendar,
   typically a meeting, appointment, reminder, or anniversary.  It is
   required to start at a certain point in time and typically has a non-
   zero duration.  Multiple participants may partake in the event at
   multiple locations.

   The @type (Section 4.1.1) property value MUST be "Event".

2.2.  Task

   Media type: "application/jscalendar+json;type=task"

   A Task represents an action item, assignment, to-do item, or work
   item.  It may start and be due at certain points in time, take some
   estimated time to complete, and recur, none of which is required.

   The @type (Section 4.1.1) property value MUST be "Task".

2.3.  Group

   Media type: "application/jscalendar+json;type=group"

   A Group is a collection of Event (Section 2.1) and/or Task
   (Section 2.2) objects.  Typically, objects are grouped by topic
   (e.g., by keywords) or calendar membership.

   The @type (Section 4.1.1) property value MUST be "Group".

3.  Structure of JSCalendar Objects

   A JSCalendar object is a JSON object [RFC8259], which MUST be valid
   I-JSON (a stricter subset of JSON) [RFC7493].  Property names and
   values are case sensitive.

   The object has a collection of properties, as specified in the
   following sections.  Properties are specified as being either
   mandatory or optional.  Optional properties may have a default value
   if explicitly specified in the property definition.

3.1.  Object Type

   JSCalendar objects MUST name their type in the "@type" property if
   not explicitly specified otherwise for the respective object type.  A
   notable exception to this rule is the PatchObject (Section 1.4.9).

3.2.  Normalization and Equivalence

   JSCalendar aims to provide unambiguous definitions for value types
   and properties but does not define a general normalization or
   equivalence method for JSCalendar objects and types.  This is because
   the notion of equivalence might range from byte-level equivalence to
   semantic equivalence, depending on the respective use case.
   Normalization of JSCalendar objects is hindered because of the
   following reasons:

   *  Custom JSCalendar properties may contain arbitrary JSON values,
      including arrays.  However, equivalence of arrays might or might
      not depend on the order of elements, depending on the respective
      property definition.

   *  Several JSCalendar property values are defined as URIs and media
      types, but normalization of these types is inherently protocol and
      scheme specific, depending on the use case of the equivalence
      definition (see Section 6 of [RFC3986]).

   Considering this, the definition of equivalence and normalization is
   left to client and server implementations and to be negotiated by a
   calendar exchange protocol or defined elsewhere.

3.3.  Vendor-Specific Property Extensions, Values, and Types

   Vendors MAY add additional properties to the calendar object to
   support their custom features.  To avoid conflict, the names of these
   properties MUST be prefixed by a domain name controlled by the vendor
   followed by a colon, e.g., "example.com:customprop".  If the value is
   a new JSCalendar object, it either MUST include an "@type" property,
   or it MUST explicitly be specified to not require a type designator.
   The type name MUST be prefixed with a domain name controlled by the
   vendor.

   Some JSCalendar properties allow vendor-specific value extensions.
   Such vendor-specific values MUST be prefixed by a domain name
   controlled by the vendor followed by a colon, e.g.,
   "example.com:customrel".

   Vendors are strongly encouraged to register any new property values
   or extensions that are useful to other systems as well, rather than
   use a vendor-specific prefix.

4.  Common JSCalendar Properties

   This section describes the properties that are common to the various
   JSCalendar object types.  Specific JSCalendar object types may only
   support a subset of these properties.  The object type definitions in
   Section 5 describe the set of supported properties per type.

4.1.  Metadata Properties

4.1.1.  @type

   Type: "String" (mandatory)

   This specifies the type that this object represents.  The allowed
   value differs by object type and is defined in Sections 2.1, 2.2, and
   2.3.

4.1.2.  uid

   Type: "String" (mandatory)

   This is a globally unique identifier used to associate objects
   representing the same event, task, group, or other object across
   different systems, calendars, and views.  For recurring events and
   tasks, the UID is associated with the base object and therefore is
   the same for all occurrences; the combination of the UID with a
   "recurrenceId" identifies a particular instance.

   The generator of the identifier MUST guarantee that the identifier is
   unique.  [RFC4122] describes a range of established algorithms to
   generate universally unique identifiers (UUIDs).  UUID version 4,
   described in Section 4.4 of [RFC4122], is RECOMMENDED.

   For compatibility with UIDs [RFC5545], implementations MUST be able
   to receive and persist values of at least 255 octets for this
   property, but they MUST NOT truncate values in the middle of a UTF-8
   multi-octet sequence.

4.1.3.  relatedTo

   Type: "String[Relation]" (optional)

   This relates the object to other JSCalendar objects.  This is
   represented as a map of the UIDs of the related objects to
   information about the relation.

   If an object is split to make a "this and future" change to a
   recurrence, the original object MUST be truncated to end at the
   previous occurrence before this split, and a new object is created to
   represent all the occurrences after the split.  A "next" relation
   MUST be set on the original object's "relatedTo" property for the UID
   of the new object.  A "first" relation for the UID of the first
   object in the series MUST be set on the new object.  Clients can then
   follow these UIDs to get the complete set of objects if the user
   wishes to modify them all at once.

4.1.4.  prodId

   Type: "String" (optional)

   This is the identifier for the product that last updated the
   JSCalendar object.  This should be set whenever the data in the
   object is modified (i.e., whenever the "updated" property is set).

   The vendor of the implementation MUST ensure that this is a globally
   unique identifier, using some technique such as a Formal Public
   Identifier (FPI) value, as defined in [ISO.9070.1991].

   This property SHOULD NOT be used to alter the interpretation of a
   JSCalendar object beyond the semantics specified in this document.
   For example, it is not to be used to further the understanding of
   nonstandard properties, a practice that is known to cause long-term
   interoperability problems.

4.1.5.  created

   Type: "UTCDateTime" (optional)

   This is the date and time this object was initially created.

4.1.6.  updated

   Type: "UTCDateTime" (mandatory)

   This is the date and time the data in this object was last modified
   (or its creation date/time if not modified since).

4.1.7.  sequence

   Type: "UnsignedInt" (optional, default: 0)

   Initially zero, this MUST be incremented by one every time a change
   is made to the object, except if the change only modifies the
   "participants" property (see Section 4.4.6).

   This is used as part of the iCalendar Transport-independent
   Interoperability Protocol (iTIP) [RFC5546] to know which version of
   the object a scheduling message relates to.

4.1.8.  method

   Type: "String" (optional)

   This is the iTIP [RFC5546] method, in lowercase.  This MUST only be
   present if the JSCalendar object represents an iTIP scheduling
   message.

4.2.  What and Where Properties

4.2.1.  title

   Type: "String" (optional, default: empty String)

   This is a short summary of the object.

4.2.2.  description

   Type: "String" (optional, default: empty String)

   This is a longer-form text description of the object.  The content is
   formatted according to the "descriptionContentType" property.

4.2.3.  descriptionContentType

   Type: "String" (optional, default: "text/plain")

   This describes the media type [RFC6838] of the contents of the
   "description" property.  Media types MUST be subtypes of type "text"
   and SHOULD be "text/plain" or "text/html" [MEDIATYPES].  They MAY
   include parameters, and the "charset" parameter value MUST be "utf-
   8", if specified.  Descriptions of type "text/html" MAY contain "cid"
   URLs [RFC2392] to reference links in the calendar object by use of
   the "cid" property of the Link object.

4.2.4.  showWithoutTime

   Type: "Boolean" (optional, default: false)

   This indicates that the time is not important to display to the user
   when rendering this calendar object.  An example of this is an event
   that conceptually occurs all day or across multiple days, such as
   "New Year's Day" or "Italy Vacation".  While the time component is
   important for free-busy calculations and checking for scheduling
   clashes, calendars may choose to omit displaying it and/or display
   the object separately to other objects to enhance the user's view of
   their schedule.

   Such events are also commonly known as "all-day" events.

4.2.5.  locations

   Type: "Id[Location]" (optional)

   This is a map of location ids to Location objects, representing
   locations associated with the object.

   A Location object has the following properties.  It MUST have at
   least one property other than the "relativeTo" property.

   @type: "String" (mandatory)
      This specifies the type of this object.  This MUST be "Location".

   name: "String" (optional)
      This is the human-readable name of the location.

   description: "String" (optional)
      This is the human-readable, plain-text instructions for accessing
      this location.  This may be an address, set of directions, door
      access code, etc.

   locationTypes: "String[Boolean]" (optional)
      This is a set of one or more location types that describe this
      location.  All types MUST be from the "Location Types Registry"
      [LOCATIONTYPES], as defined in [RFC4589].  The set is represented
      as a map, with the keys being the location types.  The value for
      each key in the map MUST be true.

   relativeTo: "String" (optional)
      This specifies the relation between this location and the time of
      the JSCalendar object.  This is primarily to allow events
      representing travel to specify the location of departure (at the
      start of the event) and location of arrival (at the end); this is
      particularly important if these locations are in different time
      zones, as a client may wish to highlight this information for the
      user.

      This MUST be one of the following values, another value registered
      in the IANA "JSCalendar Enum Values" registry, or a vendor-
      specific value (see Section 3.3).  Any value the client or server
      doesn't understand should be treated the same as if this property
      is omitted.

      "start":  The event/task described by this JSCalendar object
         occurs at this location at the time the event/task starts.

      "end":  The event/task described by this JSCalendar object occurs
         at this location at the time the event/task ends.

   timeZone: "TimeZoneId" (optional)
      This is a time zone for this location.

   coordinates: "String" (optional)
      This is a "geo:" URI [RFC5870] for the location.

   links: "Id[Link]" (optional)
      This is a map of link ids to Link objects, representing external
      resources associated with this location, for example, a vCard or
      image.  If there are no links, this MUST be omitted (rather than
      specified as an empty set).

4.2.6.  virtualLocations

   Type: "Id[VirtualLocation]" (optional)

   This is a map of virtual location ids to VirtualLocation objects,
   representing virtual locations, such as video conferences or chat
   rooms, associated with the object.

   A VirtualLocation object has the following properties.

   @type: "String" (mandatory)
      This specifies the type of this object.  This MUST be
      "VirtualLocation".

   name: "String" (optional, default: empty String)
      This is the human-readable name of the virtual location.

   description: "String" (optional)
      These are human-readable plain-text instructions for accessing
      this virtual location.  This may be a conference access code, etc.

   uri: "String" (mandatory)
      This is a URI [RFC3986] that represents how to connect to this
      virtual location.

      This may be a telephone number (represented using the "tel:"
      scheme, e.g., "tel:+1-555-555-5555") for a teleconference, a web
      address for online chat, or any custom URI.

   features: "String[Boolean]" (optional)
      A set of features supported by this virtual location.  The set is
      represented as a map, with the keys being the feature.  The value
      for each key in the map MUST be true.

      The feature MUST be one of the following values, another value
      registered in the IANA "JSCalendar Enum Values" registry, or a
      vendor-specific value (see Section 3.3).  Any value the client or
      server doesn't understand should be treated the same as if this
      feature is omitted.

      audio:  Audio conferencing

      chat:  Chat or instant messaging

      feed:  Blog or atom feed

      moderator:  Provides moderator-specific features

      phone:  Phone conferencing

      screen:  Screen sharing

      video:  Video conferencing

4.2.7.  links

   Type: "Id[Link]" (optional)

   This is a map of link ids to Link objects, representing external
   resources associated with the object.

   Links with a rel of "enclosure" MUST be considered by the client to
   be attachments for download.

   Links with a rel of "describedby" MUST be considered by the client to
   be alternative representations of the description.

   Links with a rel of "icon" MUST be considered by the client to be
   images that it may use when presenting the calendar data to a user.
   The "display" property may be set to indicate the purpose of this
   image.

4.2.8.  locale

   Type: "String" (optional)

   This is the language tag, as defined in [RFC5646], that best
   describes the locale used for the text in the calendar object, if
   known.

4.2.9.  keywords

   Type: "String[Boolean]" (optional)

   This is a set of keywords or tags that relate to the object.  The set
   is represented as a map, with the keys being the keywords.  The value
   for each key in the map MUST be true.

4.2.10.  categories

   Type: "String[Boolean]" (optional)

   This is a set of categories that relate to the calendar object.  The
   set is represented as a map, with the keys being the categories
   specified as URIs.  The value for each key in the map MUST be true.

   In contrast to keywords, categories are typically structured.  For
   example, a vendor owning the domain "example.com" might define the
   categories "http://example.com/categories/sports/american-football"
   and "http://example.com/categories/music/r-b".

4.2.11.  color

   Type: "String" (optional)

   This is a color clients MAY use when displaying this calendar object.
   The value is a color name taken from the set of names defined in
   Section 4.3 of CSS Color Module Level 3 [COLORS] or an RGB value in
   hexadecimal notation, as defined in Section 4.2.1 of CSS Color Module
   Level 3.

4.3.  Recurrence Properties

   Some events and tasks occur at regular or irregular intervals.
   Rather than having to copy the data for every occurrence, there can
   be a base event with rules to generate recurrences and/or overrides
   that add extra dates or exceptions to the rules.

   The recurrence set is the complete set of instances for an object.
   It is generated by considering the following properties in order, all
   of which are optional:

   1.  The "recurrenceRules" property (Section 4.3.3) generates a set of
       extra date-times on which the object occurs.

   2.  The "excludedRecurrenceRules" property (Section 4.3.4) generates
       a set of date-times that are to be removed from the previously
       generated set of date-times on which the object occurs.

   3.  The "recurrenceOverrides" property (Section 4.3.5) defines date-
       times that are added or excluded to form the final set.  (This
       property may also contain changes to the object to apply to
       particular instances.)

4.3.1.  recurrenceId

   Type: "LocalDateTime" (optional)

   If present, this JSCalendar object represents one occurrence of a
   recurring JSCalendar object.  If present, the "recurrenceRules" and
   "recurrenceOverrides" properties MUST NOT be present.

   The value is a date-time either produced by the "recurrenceRules" of
   the base event or added as a key to the "recurrenceOverrides"
   property of the base event.

4.3.2.  recurrenceIdTimeZone

   Type: "TimeZoneId|null" (optional, default: null)

   Identifies the time zone of the main JSCalendar object, of which this
   JSCalendar object is a recurrence instance.  This property MUST be
   set if the "recurrenceId" property is set.  It MUST NOT be set if the
   "recurrenceId" property is not set.

4.3.3.  recurrenceRules

   Type: "RecurrenceRule[]" (optional)

   This defines a set of recurrence rules (repeating patterns) for
   recurring calendar objects.

   An Event recurs by applying the recurrence rules to the "start" date-
   time.

   A Task recurs by applying the recurrence rules to the "start" date-
   time, if defined; otherwise, it recurs by the "due" date-time, if
   defined.  If the task defines neither a "start" nor "due" date-time,
   it MUST NOT define a "recurrenceRules" property.

   If multiple recurrence rules are given, each rule is to be applied,
   and then the union of the results are used, ignoring any duplicates.

   A RecurrenceRule object is a JSON object mapping of a RECUR value
   type in iCalendar [RFC5545] [RFC7529] and has the same semantics.  It
   has the following properties:

   @type: "String" (mandatory)
      This specifies the type of this object.  This MUST be
      "RecurrenceRule".

   frequency: "String" (mandatory)
      This is the time span covered by each iteration of this recurrence
      rule (see Section 4.3.3.1 for full semantics).  This MUST be one
      of the following values:

      *  "yearly"

      *  "monthly"

      *  "weekly"

      *  "daily"

      *  "hourly"

      *  "minutely"

      *  "secondly"

      This is the FREQ part from iCalendar, converted to lowercase.

   interval: "UnsignedInt" (optional, default: 1)
      This is the interval of iteration periods at which the recurrence
      repeats.  If included, it MUST be an integer >= 1.

      This is the INTERVAL part from iCalendar.

   rscale: "String" (optional, default: "gregorian")
      This is the calendar system in which this recurrence rule
      operates, in lowercase.  This MUST be either a CLDR-registered
      calendar system name [CLDR] or a vendor-specific value (see
      Section 3.3).

      This is the RSCALE part from iCalendar RSCALE [RFC7529], converted
      to lowercase.

   skip: "String" (optional, default: "omit")
      This is the behavior to use when the expansion of the recurrence
      produces invalid dates.  This property only has an effect if the
      frequency is "yearly" or "monthly".  It MUST be one of the
      following values:

      *  "omit"

      *  "backward"

      *  "forward"

      This is the SKIP part from iCalendar RSCALE [RFC7529], converted
      to lowercase.

   firstDayOfWeek: "String" (optional, default: "mo")
      This is the day on which the week is considered to start,
      represented as a lowercase, abbreviated, and two-letter English
      day of the week.  If included, it MUST be one of the following
      values:

      *  "mo"

      *  "tu"

      *  "we"

      *  "th"

      *  "fr"

      *  "sa"

      *  "su"

      This is the WKST part from iCalendar.

   byDay: "NDay[]" (optional)
      These are days of the week on which to repeat.  An "NDay" object
      has the following properties:

      @type: "String" (mandatory)
         This specifies the type of this object.  This MUST be "NDay".

      day: "String" (mandatory)
         This is a day of the week on which to repeat; the allowed
         values are the same as for the "firstDayOfWeek" recurrenceRule
         property.

         This is the day of the week of the BYDAY part in iCalendar,
         converted to lowercase.

      nthOfPeriod: "Int" (optional)
         If present, rather than representing every occurrence of the
         weekday defined in the "day" property, it represents only a
         specific instance within the recurrence period.  The value can
         be positive or negative but MUST NOT be zero.  A negative
         integer means the nth-last occurrence within that period (i.e.,
         -1 is the last occurrence, -2 the one before that, etc.).

         This is the ordinal part of the BYDAY value in iCalendar (e.g.,
         1 or -3).

   byMonthDay: "Int[]" (optional)
      These are the days of the month on which to repeat.  Valid values
      are between 1 and the maximum number of days any month may have in
      the calendar given by the "rscale" property and the negative
      values of these numbers.  For example, in the Gregorian calendar,
      valid values are 1 to 31 and -31 to -1.  Negative values offset
      from the end of the month.  The array MUST have at least one entry
      if included.

      This is the BYMONTHDAY part in iCalendar.

   byMonth: "String[]" (optional)
      These are the months in which to repeat.  Each entry is a string
      representation of a number, starting from "1" for the first month
      in the calendar (e.g., "1" means January with the Gregorian
      calendar), with an optional "L" suffix (see [RFC7529]) for leap
      months (this MUST be uppercase, e.g., "3L").  The array MUST have
      at least one entry if included.

      This is the BYMONTH part from iCalendar.

   byYearDay: "Int[]" (optional)
      These are the days of the year on which to repeat.  Valid values
      are between 1 and the maximum number of days any year may have in
      the calendar given by the "rscale" property and the negative
      values of these numbers.  For example, in the Gregorian calendar,
      valid values are 1 to 366 and -366 to -1.  Negative values offset
      from the end of the year.  The array MUST have at least one entry
      if included.

      This is the BYYEARDAY part from iCalendar.

   byWeekNo: "Int[]" (optional)
      These are the weeks of the year in which to repeat.  Valid values
      are between 1 and the maximum number of weeks any year may have in
      the calendar given by the "rscale" property and the negative
      values of these numbers.  For example, in the Gregorian calendar,
      valid values are 1 to 53 and -53 to -1.  The array MUST have at
      least one entry if included.

      This is the BYWEEKNO part from iCalendar.

   byHour: "UnsignedInt[]" (optional)
      These are the hours of the day in which to repeat.  Valid values
      are 0 to 23.  The array MUST have at least one entry if included.
      This is the BYHOUR part from iCalendar.

   byMinute: "UnsignedInt[]" (optional)
      These are the minutes of the hour in which to repeat.  Valid
      values are 0 to 59.  The array MUST have at least one entry if
      included.

      This is the BYMINUTE part from iCalendar.

   bySecond: "UnsignedInt[]" (optional)
      These are the seconds of the minute in which to repeat.  Valid
      values are 0 to 60.  The array MUST have at least one entry if
      included.

      This is the BYSECOND part from iCalendar.

   bySetPosition: "Int[]" (optional)
      These are the occurrences within the recurrence interval to
      include in the final results.  Negative values offset from the end
      of the list of occurrences.  The array MUST have at least one
      entry if included.  This is the BYSETPOS part from iCalendar.

   count: "UnsignedInt" (optional)
      These are the number of occurrences at which to range-bound the
      recurrence.  This MUST NOT be included if an "until" property is
      specified.

      This is the COUNT part from iCalendar.

   until: "LocalDateTime" (optional)
      These are the date-time at which to finish recurring.  The last
      occurrence is on or before this date-time.  This MUST NOT be
      included if a "count" property is specified.  Note that if not
      specified otherwise for a specific JSCalendar object, this date is
      to be interpreted in the time zone specified in the JSCalendar
      object's "timeZone" property.

      This is the UNTIL part from iCalendar.

4.3.3.1.  Interpreting Recurrence Rules

   A recurrence rule specifies a set of date-times for recurring
   calendar objects.  A recurrence rule has the following semantics.
   Note that wherever "year", "month", or "day of month" is used, this
   is within the calendar system given by the "rscale" property, which
   defaults to "gregorian" if omitted.

   1.  A set of candidates is generated.  This is every second within a
       period defined by the "frequency" property value:

       "yearly":  every second from midnight on the first day of a year
          (inclusive) to midnight the first day of the following year
          (exclusive).

          If skip is not "omit", the calendar system has leap months,
          and there is a "byMonth" property, generate candidates for the
          leap months, even if they don't occur in this year.

          If skip is not "omit" and there is a "byMonthDay" property,
          presume each month has the maximum number of days any month
          may have in this calendar system when generating candidates,
          even if it's more than this month actually has.

       "monthly":  every second from midnight on the first day of a
          month (inclusive) to midnight on the first of the following
          month (exclusive).

          If skip is not "omit" and there is a "byMonthDay" property,
          presume the month has the maximum number of days any month may
          have in this calendar system when generating candidates, even
          if it's more than this month actually has.

       "weekly":  every second from midnight (inclusive) on the first
          day of the week (as defined by the "firstDayOfWeek" property
          or Monday if omitted) to midnight seven days later
          (exclusive).

       "daily":  every second from midnight at the start of the day
          (inclusive) to midnight at the end of the day (exclusive).

       "hourly":  every second from the beginning of the hour
          (inclusive) to the beginning of the next hour (exclusive).

       "minutely":  every second from the beginning of the minute
          (inclusive) to the beginning of the next minute (exclusive).

       "secondly":  only the second itself.

   2.  Each date-time candidate is compared against all of the byX
       properties of the rule except bySetPosition.  If any property in
       the rule does not match the date-time, the date-time is
       eliminated.  Each byX property is an array; the date-time matches
       the property if it matches any of the values in the array.  The
       properties have the following semantics:

       byMonth:  The date-time is in the given month.

       byWeekNo:  The date-time is in the nth week of the year.
          Negative numbers mean the nth last week of the year.  This
          corresponds to weeks according to week numbering, as defined
          in ISO.8601.2004, with a week defined as a seven-day period,
          starting on the "firstDayOfWeek" property value or Monday if
          omitted.  Week number one of the calendar year is the first
          week that contains at least four days in that calendar year.

          If the date-time is not valid (this may happen when generating
          candidates with a "skip" property in effect), it is always
          eliminated by this property.

       byYearDay:  The date-time is on the nth day of year.  Negative
          numbers mean the nth last day of the year.

          If the date-time is not valid (this may happen when generating
          candidates with a "skip" property in effect), it is always
          eliminated by this property.

       byMonthDay:  The date-time is on the given day of the month.
          Negative numbers mean the nth last day of the month.

       byDay:  The date-time is on the given day of the week.  If the
          day is prefixed by a number, it is the nth occurrence of that
          day of the week within the month (if frequency is monthly) or
          year (if frequency is yearly).  Negative numbers mean the nth
          last occurrence within that period.

       byHour:  The date-time has the given hour value.

       byMinute:  The date-time has the given minute value.

       bySecond:  The date-time has the given second value.

       If a "skip" property is defined and is not "omit", there may be
       candidates that do not correspond to valid dates (e.g., February
       31st in the Gregorian calendar).  In this case, the properties
       MUST be considered in the order above, and:

       1.  After applying the byMonth filter, if the candidate's month
           is invalid for the given year, increment it (if skip is
           "forward") or decrement it (if skip is "backward") until a
           valid month is found, incrementing/decrementing the year as
           well if passing through the beginning/end of the year.  This
           only applies to calendar systems with leap months.

       2.  After applying the byMonthDay filter, if the day of the month
           is invalid for the given month and year, change the date to
           the first day of the next month (if skip is "forward") or the
           last day of the current month (if skip is "backward").

       3.  If any valid date produced after applying the skip is already
           a candidate, eliminate the duplicate.  (For example, after
           adjusting, February 30th and February 31st would both become
           the same "real" date, so one is eliminated as a duplicate.)

   3.  If a "bySetPosition" property is included, this is now applied to
       the ordered list of remaining dates.  This property specifies the
       indexes of date-times to keep; all others should be eliminated.
       Negative numbers are indexed from the end of the list, with -1
       being the last item, -2 the second from last, etc.

   4.  Any date-times before the start date of the event are eliminated
       (see below for why this might be needed).

   5.  If a "skip" property is included and is not "omit", eliminate any
       date-times that have already been produced by previous iterations
       of the algorithm.  (This is not possible if skip is "omit".)

   6.  If further dates are required (we have not reached the until date
       or count limit), skip the next (interval - 1) sets of candidates,
       then continue from step 1.

   When determining the set of occurrence dates for an event or task,
   the following extra rules must be applied:

   1.  The initial date-time to which the rule is applied (the "start"
       date-time for events or the "start" or "due" date-time for tasks)
       is always the first occurrence in the expansion (and is counted
       if the recurrence is limited by a "count" property), even if it
       would normally not match the rule.

   2.  The first set of candidates to consider is that which would
       contain the initial date-time.  This means the first set may
       include candidates before the initial date-time; such candidates
       are eliminated from the results in step 4 of the list above.

   3.  The following properties MUST be implicitly added to the rule
       under the given conditions:

       *  If frequency is not "secondly" and there is no "bySecond"
          property, add a "bySecond" property with the sole value being
          the seconds value of the initial date-time.

       *  If frequency is not "secondly" or "minutely" and there is no
          "byMinute" property, add a "byMinute" property with the sole
          value being the minutes value of the initial date-time.

       *  If frequency is not "secondly", "minutely", or "hourly" and
          there is no "byHour" property, add a "byHour" property with
          the sole value being the hours value of the initial date-time.

       *  If frequency is "weekly" and there is no "byDay" property, add
          a "byDay" property with the sole value being the day of the
          week of the initial date-time.

       *  If frequency is "monthly" and there is no "byDay" property and
          no "byMonthDay" property, add a "byMonthDay" property with the
          sole value being the day of the month of the initial date-
          time.

       *  If frequency is "yearly" and there is no "byYearDay" property:

          -  If there are no "byMonth" or "byWeekNo" properties, and
             either there is a "byMonthDay" property or there is no
             "byDay" property, add a "byMonth" property with the sole
             value being the month of the initial date-time.

          -  If there are no "byMonthDay", "byWeekNo", or "byDay"
             properties, add a "byMonthDay" property with the sole value
             being the day of the month of the initial date-time.

          -  If there is a "byWeekNo" property and no "byMonthDay" or
             "byDay" properties, add a "byDay" property with the sole
             value being the day of the week of the initial date-time.

4.3.4.  excludedRecurrenceRules

   Type: "RecurrenceRule[]" (optional)

   This defines a set of recurrence rules (repeating patterns) for date-
   times on which the object will not occur.  The rules are interpreted
   the same as for the "recurrenceRules" property (see Section 4.3.3),
   with the exception that the initial date-time to which the rule is
   applied (the "start" date-time for events or the "start" or "due"
   date-time for tasks) is only considered part of the expansion if it
   matches the rule.  The resulting set of date-times is then removed
   from those generated by the "recurrenceRules" property, as described
   in Section 4.3.

4.3.5.  recurrenceOverrides

   Type: "LocalDateTime[PatchObject]" (optional)

   Maps recurrence ids (the date-time produced by the recurrence rule)
   to the overridden properties of the recurrence instance.

   If the recurrence id does not match a date-time from the recurrence
   rule (or no rule is specified), it is to be treated as an additional
   occurrence (like an RDATE from iCalendar).  The patch object may
   often be empty in this case.

   If the patch object defines the "excluded" property of an occurrence
   to be true, this occurrence is omitted from the final set of
   recurrences for the calendar object (like an EXDATE from iCalendar).
   Such a patch object MUST NOT patch any other property.

   By default, an occurrence inherits all properties from the main
   object except the start (or due) date-time, which is shifted to match
   the recurrence id LocalDateTime.  However, individual properties of
   the occurrence can be modified by a patch or multiple patches.  It is
   valid to patch the "start" property value, and this patch takes
   precedence over the value generated from the recurrence id.  Both the
   recurrence id as well as the patched "start" date-time may occur
   before the original JSCalendar object's "start" or "due" date.

   A pointer in the PatchObject MUST be ignored if it starts with one of
   the following prefixes:

   *  @type

   *  excludedRecurrenceRules

   *  method

   *  privacy

   *  prodId

   *  recurrenceId

   *  recurrenceIdTimeZone

   *  recurrenceOverrides

   *  recurrenceRules

   *  relatedTo

   *  replyTo

   *  sentBy

   *  timeZones

   *  uid

4.3.6.  excluded

   Type: "Boolean" (optional, default: false)

   This defines if this object is an overridden, excluded instance of a
   recurring JSCalendar object (see Section 4.3.5).  If this property
   value is true, this calendar object instance MUST be removed from the
   occurrence expansion.  The absence of this property, or the presence
   of its default value as false, indicates that this instance MUST be
   included in the occurrence expansion.

4.4.  Sharing and Scheduling Properties

4.4.1.  priority

   Type: "Int" (optional, default: 0)

   This specifies a priority for the calendar object.  This may be used
   as part of scheduling systems to help resolve conflicts for a time
   period.

   The priority is specified as an integer in the range 0 to 9.  A value
   of 0 specifies an undefined priority, for which the treatment will
   vary by situation.  A value of 1 is the highest priority.  A value of
   2 is the second highest priority.  Subsequent numbers specify a
   decreasing ordinal priority.  A value of 9 is the lowest priority.
   Other integer values are reserved for future use.

4.4.2.  freeBusyStatus

   Type: "String" (optional, default: "busy")

   This specifies how this calendar object should be treated when
   calculating free-busy state.  This MUST be one of the following
   values, another value registered in the IANA "JSCalendar Enum Values"
   registry, or a vendor-specific value (see Section 3.3):

   "free":  The object should be ignored when calculating whether the
      user is busy.

   "busy":  The object should be included when calculating whether the
      user is busy.

4.4.3.  privacy

   Type: "String" (optional, default: "public")

   Calendar objects are normally collected together and may be shared
   with other users.  The privacy property allows the object owner to
   indicate that it should not be shared or should only have the time
   information shared but the details withheld.  Enforcement of the
   restrictions indicated by this property is up to the API via which
   this object is accessed.

   This property MUST NOT affect the information sent to scheduled
   participants; it is only interpreted by protocols that share the
   calendar objects belonging to one user with other users.

   The value MUST be one of the following values, another value
   registered in the IANA "JSCalendar Enum Values" registry, or a
   vendor-specific value (see Section 3.3).  Any value the client or
   server doesn't understand should be preserved but treated as
   equivalent to "private".

   "public":  The full details of the object are visible to those whom
      the object's calendar is shared with.

   "private":  The details of the object are hidden; only the basic time
      and metadata are shared.  The following properties MAY be shared;
      any other properties MUST NOT be shared:

      *  @type

      *  created

      *  due

      *  duration

      *  estimatedDuration

      *  freeBusyStatus

      *  privacy

      *  recurrenceOverrides (Only patches that apply to another
         permissible property are allowed to be shared.)

      *  sequence

      *  showWithoutTime

      *  start

      *  timeZone

      *  timeZones

      *  uid

      *  updated

   "secret":  The object is hidden completely (as though it did not
      exist) when the calendar this object is in is shared.

4.4.4.  replyTo

   Type: "String[String]" (optional)

   This represents methods by which participants may submit their
   response to the organizer of the calendar object.  The keys in the
   property value are the available methods and MUST only contain ASCII
   alphanumeric characters (A-Za-z0-9).  The value is a URI for the
   method specified in the key.  Future methods may be defined in future
   specifications and registered with IANA; a calendar client MUST
   ignore any method it does not understand but MUST preserve the method
   key and URI.  This property MUST be omitted if no method is defined
   (rather than being specified as an empty object).

   The following methods are defined:

   "imip":  The organizer accepts an iCalendar Message-Based
      Interoperability Protocol (iMIP) [RFC6047] response at this email
      address.  The value MUST be a "mailto:" URI.

   "web":  Opening this URI in a web browser will provide the user with
      a page where they can submit a reply to the organizer.  The value
      MUST be a URL using the "https:" scheme.

   "other":  The organizer is identified by this URI, but the method for
      submitting the response is undefined.

4.4.5.  sentBy

   Type: "String" (optional)

   This is the email address in the "From" header of the email in which
   this calendar object was received.  This is only relevant if the
   calendar object is received via iMIP or as an attachment to a
   message.  If set, the value MUST be a valid "addr-spec" value as
   defined in Section 3.4.1 of [RFC5322].

4.4.6.  participants

   Type: "Id[Participant]" (optional)

   This is a map of participant ids to participants, describing their
   participation in the calendar object.

   If this property is set and any participant has a "sendTo" property,
   then the "replyTo" property of this calendar object MUST define at
   least one reply method.

   A Participant object has the following properties:

   @type: "String" (mandatory)
      This specifies the type of this object.  This MUST be
      "Participant".

   name: "String" (optional)
      This is the display name of the participant (e.g., "Joe Bloggs").

   email: "String" (optional)
      This is the email address to use to contact the participant or,
      for example, match with an address book entry.  If set, the value
      MUST be a valid "addr-spec" value as defined in Section 3.4.1 of
      [RFC5322].

   description: "String" (optional)
      This is a plain-text description of this participant.  For
      example, this may include more information about their role in the
      event or how best to contact them.

   sendTo: "String[String]" (optional)
      This represents methods by which the participant may receive the
      invitation and updates to the calendar object.

      The keys in the property value are the available methods and MUST
      only contain ASCII alphanumeric characters (A-Za-z0-9).  The value
      is a URI for the method specified in the key.  Future methods may
      be defined in future specifications and registered with IANA; a
      calendar client MUST ignore any method it does not understand but
      MUST preserve the method key and URI.  This property MUST be
      omitted if no method is defined (rather than being specified as an
      empty object).

      The following methods are defined:

      "imip":  The participant accepts an iMIP [RFC6047] request at this
         email address.  The value MUST be a "mailto:" URI.  It MAY be
         different from the value of the participant's "email" property.

      "other":  The participant is identified by this URI, but the
         method for submitting the invitation is undefined.

   kind: "String" (optional)
      This is what kind of entity this participant is, if known.

      This MUST be one of the following values, another value registered
      in the IANA "JSCalendar Enum Values" registry, or a vendor-
      specific value (see Section 3.3).  Any value the client or server
      doesn't understand should be treated the same as if this property
      is omitted.

      "individual":  a single person

      "group":  a collection of people invited as a whole

      "location":  a physical location that needs to be scheduled, e.g.,
         a conference room

      "resource":  a non-human resource other than a location, such as a
         projector

   roles: "String[Boolean]" (mandatory)
      This is a set of roles that this participant fulfills.

      At least one role MUST be specified for the participant.  The keys
      in the set MUST be one of the following values, another value
      registered in the IANA "JSCalendar Enum Values" registry, or a
      vendor-specific value (see Section 3.3):

      "owner":  The participant is an owner of the object.  This
         signifies they have permission to make changes to it that
         affect the other participants.  Nonowner participants may only
         change properties that affect only themselves (for example,
         setting their own alerts or changing their RSVP status).

      "attendee":  The participant is expected to be present at the
         event.

      "optional":  The participant's involvement with the event is
         optional.  This is expected to be primarily combined with the
         "attendee" role.

      "informational":  The participant is copied for informational
         reasons and is not expected to attend.

      "chair":  The participant is in charge of the event/task when it
         occurs.

      "contact":  The participant is someone that may be contacted for
         information about the event.

      The value for each key in the map MUST be true.  It is expected
      that no more than one of the roles "attendee" and "informational"
      be present; if more than one are given, "attendee" takes
      precedence over "informational".  Roles that are unknown to the
      implementation MUST be preserved.

   locationId: "Id" (optional)
      This is the location at which this participant is expected to be
      attending.

      If the value does not correspond to any location id in the
      "locations" property of the JSCalendar object, this MUST be
      treated the same as if the participant's locationId were omitted.

   language: "String" (optional)
      This is the language tag, as defined in [RFC5646], that best
      describes the participant's preferred language, if known.

   participationStatus: "String" (optional, default: "needs-action")
      This is the participation status, if any, of this participant.

      The value MUST be one of the following values, another value
      registered in the IANA "JSCalendar Enum Values" registry, or a
      vendor-specific value (see Section 3.3):

      "needs-action":  No status has yet been set by the participant.

      "accepted":  The invited participant will participate.

      "declined":  The invited participant will not participate.

      "tentative":  The invited participant may participate.

      "delegated":  The invited participant has delegated their
         attendance to another participant, as specified in the
         "delegatedTo" property.

   participationComment: "String" (optional)
      This is a note from the participant to explain their participation
      status.

   expectReply: "Boolean" (optional, default: false)
      If true, the organizer is expecting the participant to notify them
      of their participation status.

   scheduleAgent: "String" (optional, default: "server")
      This is who is responsible for sending scheduling messages with
      this calendar object to the participant.

      The value MUST be one of the following values, another value
      registered in the IANA "JSCalendar Enum Values" registry, or a
      vendor-specific value (see Section 3.3):

      "server":  The calendar server will send the scheduling messages.

      "client":  The calendar client will send the scheduling messages.

      "none":  No scheduling messages are to be sent to this
         participant.

   scheduleForceSend: "Boolean" (optional, default: false)
      A client may set the property on a participant to true to request
      that the server send a scheduling message to the participant when
      it would not normally do so (e.g., if no significant change is
      made the object or the scheduleAgent is set to client).  The
      property MUST NOT be stored in the JSCalendar object on the server
      or appear in a scheduling message.

   scheduleSequence: "UnsignedInt" (optional, default: 0)
      This is the sequence number of the last response from the
      participant.  If defined, this MUST be a nonnegative integer.

      This can be used to determine whether the participant has sent a
      new response following significant changes to the calendar object
      and to determine if future responses are responding to a current
      or older view of the data.

   scheduleStatus: "String[]" (optional)
      This is a list of status codes, returned from the processing of
      the most recent scheduling message sent to this participant.  The
      status codes MUST be valid "statcode" values as defined in the
      ABNF in Section 3.8.8.3 of [RFC5545].

      Servers MUST only add or change this property when they send a
      scheduling message to the participant.  Clients SHOULD NOT change
      or remove this property if it was provided by the server.  Clients
      MAY add, change, or remove the property for participants where the
      client is handling the scheduling.

      This property MUST NOT be included in scheduling messages.

   scheduleUpdated: "UTCDateTime" (optional)
      This is the timestamp for the most recent response from this
      participant.

      This is the "updated" property of the last response when using
      iTIP.  It can be compared to the "updated" property in future
      responses to detect and discard older responses delivered out of
      order.

   sentBy: "String" (optional)
      This is the email address in the "From" header of the email that
      last updated this participant via iMIP.  This SHOULD only be set
      if the email address is different to that in the mailto URI of
      this participant's "imip" method in the "sendTo" property (i.e.,
      the response was received from a different address to that which
      the invitation was sent to).  If set, the value MUST be a valid
      "addr-spec" value as defined in Section 3.4.1 of [RFC5322].

   invitedBy: "Id" (optional)
      This is the id of the participant who added this participant to
      the event/task, if known.

   delegatedTo: "Id[Boolean]" (optional)
      This is set of participant ids that this participant has delegated
      their participation to.  Each key in the set MUST be the id of a
      participant.  The value for each key in the map MUST be true.  If
      there are no delegates, this MUST be omitted (rather than
      specified as an empty set).

   delegatedFrom: "Id[Boolean]" (optional)
      This is a set of participant ids that this participant is acting
      as a delegate for.  Each key in the set MUST be the id of a
      participant.  The value for each key in the map MUST be true.  If
      there are no delegators, this MUST be omitted (rather than
      specified as an empty set).

   memberOf: "Id[Boolean]" (optional)
      This is a set of group participants that were invited to this
      calendar object, which caused this participant to be invited due
      to their membership in the group(s).  Each key in the set MUST be
      the id of a participant.  The value for each key in the map MUST
      be true.  If there are no groups, this MUST be omitted (rather
      than specified as an empty set).

   links: "Id[Link]" (optional)
      This is a map of link ids to Link objects, representing external
      resources associated with this participant, for example, a vCard
      or image.  If there are no links, this MUST be omitted (rather
      than specified as an empty set).

   progress: "String" (optional; only allowed for participants of a
   Task)
      This represents the progress of the participant for this task.  It
      MUST NOT be set if the "participationStatus" of this participant
      is any value other than "accepted".  See Section 5.2.5 for allowed
      values and semantics.

   progressUpdated: "UTCDateTime" (optional; only allowed for
   participants of a Task)
      This specifies the date-time the "progress" property was last set
      on this participant.  See Section 5.2.6 for allowed values and
      semantics.

   percentComplete: "UnsignedInt" (optional; only allowed for
   participants of a Task)
      This represents the percent completion of the participant for this
      task.  The property value MUST be a positive integer between 0 and
      100.

4.4.7.  requestStatus

   Type: "String" (optional)

   A request status as returned from processing the most recent
   scheduling request for this JSCalendar object.  The allowed values
   are defined by the ABNF definitions of "statcode", "statdesc" and
   "extdata" in Section 3.8.8.3 of [RFC5545] and the following ABNF
   [RFC5234]:

   reqstatus = statcode ";" statdesc [";" extdata]

   Servers MUST only add or change this property when they performe a
   scheduling action.  Clients SHOULD NOT change or remove this property
   if it was provided by the server.  Clients MAY add, change, or remove
   the property when the client is handling the scheduling.

   This property MUST only be included in scheduling messages according
   to the rules defined for the REQUEST-STATUS iCalendar property in
   [RFC5546].

4.5.  Alerts Properties

4.5.1.  useDefaultAlerts

   Type: "Boolean" (optional, default: false)

   If true, use the user's default alerts and ignore the value of the
   "alerts" property.  Fetching user defaults is dependent on the API
   from which this JSCalendar object is being fetched and is not defined
   in this specification.  If an implementation cannot determine the
   user's default alerts, or none are set, it MUST process the "alerts"
   property as if "useDefaultAlerts" is set to false.

4.5.2.  alerts

   Type: "Id[Alert]" (optional)

   This is a map of alert ids to Alert objects, representing alerts/
   reminders to display or send to the user for this calendar object.

   An Alert object has the following properties:

   @type: "String" (mandatory)
      This specifies the type of this object.  This MUST be "Alert".

   trigger: "OffsetTrigger|AbsoluteTrigger|UnknownTrigger"
   (mandatory)
      This defines when to trigger the alert.  New types may be defined
      in future documents.

      An "OffsetTrigger" object has the following properties:

      @type: "String" (mandatory)
         This specifies the type of this object.  This MUST be
         "OffsetTrigger".

      offset: "SignedDuration" (mandatory)
         This defines the offset at which to trigger the alert relative
         to the time property defined in the "relativeTo" property of
         the alert.  Negative durations signify alerts before the time
         property; positive durations signify alerts after the time
         property.

      relativeTo: "String" (optional, default: "start")
         This specifies the time property that the alert offset is
         relative to.  The value MUST be one of the following:

         "start":  triggers the alert relative to the start of the
            calendar object

         "end":  triggers the alert relative to the end/due time of the
            calendar object

      An "AbsoluteTrigger" object has the following properties:

      @type: "String" (mandatory)
         This specifies the type of this object.  This MUST be
         "AbsoluteTrigger".

      when: "UTCDateTime" (mandatory)
         This defines a specific UTC date-time when the alert is
         triggered.

      An "UnknownTrigger" object is an object that contains an "@type"
      property whose value is not recognized (i.e., not "OffsetTrigger"
      or "AbsoluteTrigger") plus zero or more other properties.  This is
      for compatibility with client extensions and future
      specifications.  Implementations SHOULD NOT trigger for trigger
      types they do not understand but MUST preserve them.

   acknowledged: "UTCDateTime" (optional)
      This records when an alert was last acknowledged.  This is set
      when the user has dismissed the alert; other clients that sync
      this property SHOULD automatically dismiss or suppress duplicate
      alerts (alerts with the same alert id that triggered on or before
      this date-time).

      For a recurring calendar object, setting the "acknowledged"
      property MUST NOT add a new override to the "recurrenceOverrides"
      property.  If the alert is not already overridden, the
      "acknowledged" property MUST be set on the alert in the base
      event/task.

      Certain kinds of alert action may not provide feedback as to when
      the user sees them, for example, email-based alerts.  For those
      kinds of alerts, this property MUST be set immediately when the
      alert is triggered and the action is successfully carried out.

   relatedTo: "String[Relation]" (optional)
      This relates this alert to other alerts in the same JSCalendar
      object.  If the user wishes to snooze an alert, the application
      MUST create an alert to trigger after snoozing.  This new snooze
      alert MUST set a parent relation to the identifier of the original
      alert.

   action: "String" (optional, default: "display")
      This describes how to alert the user.

      The value MUST be at most one of the following values, a value
      registered in the IANA "JSCalendar Enum Values" registry, or a
      vendor-specific value (see Section 3.3):

      "display":  The alert should be displayed as appropriate for the
         current device and user context.

      "email":  The alert should trigger an email sent out to the user,
         notifying them of the alert.  This action is typically only
         appropriate for server implementations.

4.6.  Multilingual Properties

4.6.1.  localizations

   Type: "String[PatchObject]" (optional)

   A map where each key is a language tag [RFC5646], and the
   corresponding value is a set of patches to apply to the calendar
   object in order to localize it into that locale.

   See the description of PatchObject (Section 1.4.9) for the structure
   of the PatchObject.  The patches are applied to the top-level
   calendar object.  In addition, the "locale" property of the patched
   object is set to the language tag.  All pointers for patches MUST end
   with one of the following suffixes; any patch that does not follow
   this MUST be ignored unless otherwise specified in a future RFC:

   *  title

   *  description

   *  name

   A patch MUST NOT have the prefix "recurrenceOverrides"; any
   localization of the override MUST be a patch to the "localizations"
   property inside the override instead.  For example, a patch to
   "locations/abcd1234/title" is permissible, but a patch to "uid" or
   "recurrenceOverrides/2020-01-05T14:00:00/title" is not.

   Note that this specification does not define how to maintain validity
   of localized content.  For example, a client application changing a
   JSCalendar object's "title" property might also need to update any
   localizations of this property.  Client implementations SHOULD
   provide the means to manage localizations, but how to achieve this is
   specific to the application's workflow and requirements.

4.7.  Time Zone Properties

4.7.1.  timeZone

   Type: "TimeZoneId|null" (optional, default: null)

   This identifies the time zone the object is scheduled in or is null
   for floating time.  This is either a name from the IANA Time Zone
   Database [TZDB] or the TimeZoneId of a custom time zone from the
   "timeZones" property (Section 4.7.2).  If omitted, this MUST be
   presumed to be null (i.e., floating time).

4.7.2.  timeZones

   Type: "TimeZoneId[TimeZone]" (optional)

   This maps identifiers of custom time zones to their time zone
   definitions.  The following restrictions apply for each key in the
   map:

   *  To avoid conflict with names in the IANA Time Zone Database
      [TZDB], it MUST start with the "/" character.

   *  It MUST be a valid "paramtext" value, as specified in Section 3.1
      of [RFC5545].

   *  At least one other property in the same JSCalendar object MUST
      reference a time zone using this identifier (i.e., orphaned time
      zones are not allowed).

   An identifier need only be unique to this JSCalendar object.  It MAY
   differ from the "tzId" property value of the TimeZone object it maps
   to.

   A JSCalendar object may be part of a hierarchy of other JSCalendar
   objects (say, an Event is an entry in a Group).  In this case, the
   set of time zones is the sum of the time zone definitions of this
   object and its parent objects.  If multiple time zones with the same
   identifier exist, then the definition closest to the calendar object
   in relation to its parents MUST be used.  (In context of Event, a
   time zone definition in its "timeZones" property has precedence over
   a definition of the same id in the Group).  Time zone definitions in
   any children of the calendar object MUST be ignored.

   A TimeZone object maps a VTIMEZONE component from iCalendar, and the
   semantics are as defined in [RFC5545].  A valid time zone MUST define
   at least one transition rule in the "standard" or "daylight"
   property.  Its properties are:

   @type: "String" (mandatory)
      This specifies the type of this object.  This MUST be "TimeZone".

   tzId: "String" (mandatory)
      This is the TZID property from iCalendar.  Note that this implies
      that the value MUST be a valid "paramtext" value as specified in
      Section 3.1. of [RFC5545].

   updated: "UTCDateTime" (optional)
      This is the LAST-MODIFIED property from iCalendar.

   url: "String" (optional)
      This is the TZURL property from iCalendar.

   validUntil: "UTCDateTime" (optional)
      This is the TZUNTIL property from iCalendar, specified in
      [RFC7808].

   aliases: "String[Boolean]" (optional)
      This maps the TZID-ALIAS-OF properties from iCalendar, specified
      in [RFC7808], to a JSON set of aliases.  The set is represented as
      an object, with the keys being the aliases.  The value for each
      key in the map MUST be true.

   standard: "TimeZoneRule[]" (optional)
      This the STANDARD sub-components from iCalendar.  The order MUST
      be preserved during conversion.

   daylight: "TimeZoneRule[]" (optional)
      This the DAYLIGHT sub-components from iCalendar.  The order MUST
      be preserved during conversion.

   A TimeZoneRule object maps a STANDARD or DAYLIGHT sub-component from
   iCalendar, with the restriction that, at most, one recurrence rule is
   allowed per rule.  It has the following properties:

   @type: "String" (mandatory)
      This specifies the type of this object.  This MUST be
      "TimeZoneRule".

   start: "LocalDateTime" (mandatory)
      This is the DTSTART property from iCalendar.

   offsetFrom: "String" (mandatory)
      This is the TZOFFSETFROM property from iCalendar.

   offsetTo: "String" (mandatory)
      This is the TZOFFSETTO property from iCalendar.

   recurrenceRules: "RecurrenceRule[]" (optional)
      This is the RRULE property mapped, as specified in Section 4.3.3.
      During recurrence rule evaluation, the "until" property value MUST
      be interpreted as a local time in the UTC time zone.

   recurrenceOverrides: "LocalDateTime[PatchObject]" (optional)
      This maps the RDATE properties from iCalendar.  The set is
      represented as an object, with the keys being the recurrence
      dates.  The patch object MUST be the empty JSON object ({}).

   names: "String[Boolean]" optional)
      This maps the TZNAME properties from iCalendar to a JSON set.  The
      set is represented as an object, with the keys being the names,
      excluding any "tznparam" component from iCalendar.  The value for
      each key in the map MUST be true.

   comments: "String[]" (optional)
      This maps the COMMENT properties from iCalendar.  The order MUST
      be preserved during conversion.

5.  Type-Specific JSCalendar Properties

5.1.  Event Properties

   In addition to the common JSCalendar object properties (Section 4),
   an Event has the following properties:

5.1.1.  start

   Type: "LocalDateTime" (mandatory)

   This is the date/time the event starts in the event's time zone (as
   specified in the "timeZone" property, see Section 4.7.1).

5.1.2.  duration

   Type: "Duration" (optional, default: "PT0S")

   This is the zero or positive duration of the event in the event's
   start time zone.  The end time of an event can be found by adding the
   duration to the event's start time.

   An Event MAY involve start and end locations that are in different
   time zones (e.g., a transcontinental flight).  This can be expressed
   using the "relativeTo" and "timeZone" properties of the Event's
   Location objects (see Section 4.2.5).

5.1.3.  status

   Type: "String" (optional, default: "confirmed")

   This is the scheduling status (Section 4.4) of an Event.  If set, it
   MUST be one of the following values, another value registered in the
   IANA "JSCalendar Enum Values" registry, or a vendor-specific value
   (see Section 3.3):

   "confirmed":  indicates the event is definitely happening

   "cancelled":  indicates the event has been cancelled

   "tentative":  indicates the event may happen

5.2.  Task Properties

   In addition to the common JSCalendar object properties (Section 4), a
   Task has the following properties:

5.2.1.  due

   Type: "LocalDateTime" (optional)

   This is the date/time the task is due in the task's time zone.

5.2.2.  start

   Type: "LocalDateTime" (optional)

   This the date/time the task should start in the task's time zone.

5.2.3.  estimatedDuration

   Type: "Duration" (optional)

   This specifies the estimated positive duration of time the task takes
   to complete.

5.2.4.  percentComplete

   Type: "UnsignedInt" (optional)

   This represents the percent completion of the task overall.  The
   property value MUST be a positive integer between 0 and 100.

5.2.5.  progress

   Type: "String" (optional)

   This defines the progress of this task.  If omitted, the default
   progress (Section 4.4) of a Task is defined as follows (in order of
   evaluation):

   "completed":  if the "progress" property value of all participants is
      "completed"

   "failed":  if at least one "progress" property value of a participant
      is "failed"

   "in-process":  if at least one "progress" property value of a
      participant is "in-process"

   "needs-action":  if none of the other criteria match

   If set, it MUST be one of the following values, another value
   registered in the IANA "JSCalendar Enum Values" registry, or a
   vendor-specific value (see Section 3.3):

   "needs-action":  indicates the task needs action

   "in-process":  indicates the task is in process

   "completed":  indicates the task is completed

   "failed":  indicates the task failed

   "cancelled":  indicates the task was cancelled

5.2.6.  progressUpdated

   Type: "UTCDateTime" (optional)

   This specifies the date/time the "progress" property of either the
   task overall (Section 5.2.5) or a specific participant
   (Section 4.4.6) was last updated.

   If the task is recurring and has future instances, a client may want
   to keep track of the last progress update timestamp of a specific
   task recurrence but leave other instances unchanged.  One way to
   achieve this is by overriding the "progressUpdated" property in the
   task "recurrenceOverrides" property.  However, this could produce a
   long list of timestamps for regularly recurring tasks.  An
   alternative approach is to split the Task into a current, single
   instance of Task with this instance progress update time and a future
   recurring instance.  See also Section 4.1.3 on splitting.

5.3.  Group Properties

   Group supports the following common JSCalendar properties
   (Section 4):

   *  @type

   *  uid

   *  prodId

   *  created

   *  updated

   *  title

   *  description

   *  descriptionContentType

   *  links

   *  locale

   *  keywords

   *  categories

   *  color

   *  timeZones

   In addition, the following Group-specific properties are supported:

5.3.1.  entries

   Type: "(Task|Event)[]" (mandatory)

   This is a collection of group members.  Implementations MUST ignore
   entries of unknown type.

5.3.2.  source

   Type: "String" (optional)

   This is the source from which updated versions of this group may be
   retrieved.  The value MUST be a URI.

6.  Examples

   The following examples illustrate several aspects of the JSCalendar
   data model and format.  The examples may omit mandatory or additional
   properties, which is indicated by a placeholder property with key
   "...".  While most of the examples use calendar event objects, they
   are also illustrative for tasks.

6.1.  Simple Event

   This example illustrates a simple one-time event.  It specifies a
   one-time event that begins on January 15, 2020 at 1 pm New York local
   time and ends after 1 hour.

   {
     "@type": "Event",
     "uid": "a8df6573-0474-496d-8496-033ad45d7fea",
     "updated": "2020-01-02T18:23:04Z",
     "title": "Some event",
     "start": "2020-01-15T13:00:00",
     "timeZone": "America/New_York",
     "duration": "PT1H"
   }

6.2.  Simple Task

   This example illustrates a simple task for a plain to-do item.

   {
     "@type": "Task",
     "uid": "2a358cee-6489-4f14-a57f-c104db4dc2f2",
     "updated": "2020-01-09T14:32:01Z",
     "title": "Do something"
   }

6.3.  Simple Group

   This example illustrates a simple calendar object group that contains
   an event and a task.

   {
     "@type": "Group",
     "uid": "bf0ac22b-4989-4caf-9ebd-54301b4ee51a",
     "updated": "2020-01-15T18:00:00Z",
     "name": "A simple group",
     "entries": [{
       "@type": "Event",
       "uid": "a8df6573-0474-496d-8496-033ad45d7fea",
       "updated": "2020-01-02T18:23:04Z",
       "title": "Some event",
       "start": "2020-01-15T13:00:00",
       "timeZone": "America/New_York",
       "duration": "PT1H"
     },
     {
       "@type": "Task",
       "uid": "2a358cee-6489-4f14-a57f-c104db4dc2f2",
       "updated": "2020-01-09T14:32:01Z",
       "title": "Do something"
     }]
   }

6.4.  All-Day Event

   This example illustrates an event for an international holiday.  It
   specifies an all-day event on April 1 that occurs every year since
   the year 1900.

   {
     "...": "",
     "title": "April Fool's Day",
     "showWithoutTime": true,
     "start": "1900-04-01T00:00:00",
     "duration": "P1D",
     "recurrenceRules": [{
       "@type": "RecurrenceRule",
       "frequency": "yearly"
     }]
   }

6.5.  Task with a Due Date

   This example illustrates a task with a due date.  It is a reminder to
   buy groceries before 6 pm Vienna local time on January 19, 2020.  The
   calendar user expects to need 1 hour for shopping.

   {
     "...": "",
     "title": "Buy groceries",
     "due": "2020-01-19T18:00:00",
     "timeZone": "Europe/Vienna",
     "estimatedDuration": "PT1H"
   }

6.6.  Event with End Time Zone

   This example illustrates the use of end time zones by use of an
   international flight.  The flight starts on April 1, 2020 at 9 am in
   Berlin local time.  The duration of the flight is scheduled at 10
   hours 30 minutes.  The time at the flight's destination is in the
   same time zone as Tokyo.  Calendar clients could use the end time
   zone to display the arrival time in Tokyo local time and highlight
   the time zone difference of the flight.  The location names can serve
   as input for navigation systems.

   {
     "...": "",
     "title": "Flight XY51 to Tokyo",
     "start": "2020-04-01T09:00:00",
     "timeZone": "Europe/Berlin",
     "duration": "PT10H30M",
     "locations": {
       "1": {
         "@type": "Location",
         "rel": "start",
         "name": "Frankfurt Airport (FRA)"
       },
       "2": {
         "@type": "Location",
         "rel": "end",
         "name": "Narita International Airport (NRT)",
         "timeZone": "Asia/Tokyo"
       }
     }
   }

6.7.  Floating-Time Event (with Recurrence)

   This example illustrates the use of floating time.  Since January 1,
   2020, a calendar user blocks 30 minutes every day to practice yoga at
   7 am local time in whatever time zone the user is located on that
   date.

   {
     "...": "",
     "title": "Yoga",
     "start": "2020-01-01T07:00:00",
     "duration": "PT30M",
     "recurrenceRules": [{
       "@type": "RecurrenceRule",
       "frequency": "daily"
     }]
   }

6.8.  Event with Multiple Locations and Localization

   This example illustrates an event that happens at both a physical and
   a virtual location.  Fans can see a live concert on premises or
   online.  The event title and descriptions are localized.

   {
     "...": "",
     "title": "Live from Music Bowl: The Band",
     "description": "Go see the biggest music event ever!",
     "locale": "en",
     "start": "2020-07-04T17:00:00",
     "timeZone": "America/New_York",
     "duration": "PT3H",
     "locations": {
       "c0503d30-8c50-4372-87b5-7657e8e0fedd": {
         "@type": "Location",
         "name": "The Music Bowl",
         "description": "Music Bowl, Central Park, New York",
         "coordinates": "geo:40.7829,-73.9654"
       }
     },
     "virtualLocations": {
       "vloc1": {
         "@type": "VirtualLocation",
         "name": "Free live Stream from Music Bowl",
         "uri": "https://stream.example.com/the_band_2020"
       }
     },
     "localizations": {
       "de": {
         "title": "Live von der Music Bowl: The Band!",
         "description": "Schau dir das größte Musikereignis an!",
         "virtualLocations/vloc1/name":
           "Gratis Live-Stream aus der Music Bowl"
       }
     }
   }

6.9.  Recurring Event with Overrides

   This example illustrates the use of recurrence overrides.  A math
   course at a university is held for the first time on January 8, 2020
   at 9 am London time and occurs every week until June 24, 2020.  Each
   lecture lasts for one hour and 30 minutes and is located at the
   Mathematics department.  This event has exceptional occurrences: at
   the last occurrence of the course is an exam, which lasts for 2 hours
   and starts at 10 am.  Also, the location of the exam differs from the
   usual location.  On April 1, no course is held.  On January 7 at 2
   pm, there is an optional introduction course, which occurs before the
   first regular lecture.

   {
     "...": "",
     "title": "Calculus I",
     "start": "2020-01-08T09:00:00",
     "timeZone": "Europe/London",
     "duration": "PT1H30M",
     "locations": {
       "mlab": {
         "@type": "Location",
         "title": "Math lab room 1",
         "description": "Math Lab I, Department of Mathematics"
       }
     },
     "recurrenceRules": [{
       "@type": "RecurrenceRule",
       "frequency": "weekly",
       "until": "2020-06-24T09:00:00"
     }],
     "recurrenceOverrides": {
       "2020-01-07T14:00:00": {
         "title": "Introduction to Calculus I (optional)"
       },
       "2020-04-01T09:00:00": {
         "excluded": true
       },
       "2020-06-25T09:00:00": {
         "title": "Calculus I Exam",
         "start": "2020-06-25T10:00:00",
         "duration": "PT2H",
         "locations": {
           "auditorium": {
             "@type": "Location",
             "title": "Big Auditorium",
             "description": "Big Auditorium, Other Road"
           }
         }
       }
     }
   }

6.10.  Recurring Event with Participants

   This example illustrates scheduled events.  A team meeting occurs
   every week since January 8, 2020 at 9 am Johannesburg time.  The
   event owner also chairs the event.  Participants meet in a virtual
   meeting room.  An attendee has accepted the invitation, but, on March
   4, 2020, he is unavailable and declined participation for this
   occurrence.

   {
     "...": "",
     "title": "FooBar team meeting",
     "start": "2020-01-08T09:00:00",
     "timeZone": "Africa/Johannesburg",
     "duration": "PT1H",
     "virtualLocations": {
       "0": {
         "@type": "VirtualLocation",
         "name": "ChatMe meeting room",
         "uri": "https://chatme.example.com?id=1234567&pw=a8a24627b63d"
       }
     },
     "recurrenceRules": [{
       "@type": "RecurrenceRule",
       "frequency": "weekly"
     }],
     "replyTo": {
       "imip": "mailto:f245f875-7f63-4a5e-a2c8@schedule.example.com"
     },
     "participants": {
       "dG9tQGZvb2Jhci5xlLmNvbQ": {
         "@type": "Participant",
         "name": "Tom Tool",
         "email": "tom@foobar.example.com",
         "sendTo": {
           "imip": "mailto:tom@calendar.example.com"
         },
         "participationStatus": "accepted",
         "roles": {
           "attendee": true
         }
       },
       "em9lQGZvb2GFtcGxlLmNvbQ": {
         "@type": "Participant",
         "name": "Zoe Zelda",
         "email": "zoe@foobar.example.com",
         "sendTo": {
           "imip": "mailto:zoe@foobar.example.com"
         },
         "participationStatus": "accepted",
         "roles": {
           "owner": true,
           "attendee": true,
           "chair": true
         }
       }
     },
     "recurrenceOverrides": {
       "2020-03-04T09:00:00": {
         "participants/dG9tQGZvb2Jhci5xlLmNvbQ/participationStatus":
                                                             "declined"
       }
     }
   }

7.  Security Considerations

   Calendaring and scheduling information is very privacy sensitive.  It
   can reveal the social network of a user, location information of this
   user and those in their social network, identity and credentials
   information, and patterns of behavior of the user in both the
   physical and cyber realm.  Additionally, calendar events and tasks
   can influence the physical location of a user or their cyber behavior
   within a known time window.  Its transmission and storage must be
   done carefully to protect it from possible threats, such as
   eavesdropping, replay, message insertion, deletion, modification, and
   on-path attacks.

   The data being stored and transmitted may be used in systems with
   real-world consequences.  For example, a home automation system may
   turn an alarm on and off or a coworking space may charge money to the
   organizer of an event that books one of their meeting rooms.  Such
   systems must be careful to authenticate all data they receive to
   prevent them from being subverted and ensure the change comes from an
   authorized entity.

   This document only defines the data format; such considerations are
   primarily the concern of the API or method of storage and
   transmission of such files.

7.1.  Expanding Recurrences

   A recurrence rule may produce infinite occurrences of an event.
   Implementations MUST handle expansions carefully to prevent
   accidental or deliberate resource exhaustion.

   Conversely, a recurrence rule may be specified that does not expand
   to anything.  It is not always possible to tell this through static
   analysis of the rule, so implementations MUST be careful to avoid
   getting stuck in infinite loops or otherwise exhausting resources
   while searching for the next occurrence.

   Events recur in the event's time zone.  If the user is in a different
   time zone, daylight saving transitions may cause an event that
   normally occurs at, for example, 9 am to suddenly shift an hour
   earlier.  This may be used in an attempt to cause a participant to
   miss an important meeting.  User agents must be careful to translate
   date-times correctly between time zones and may wish to call out
   unexpected changes in the time of a recurring event.

7.2.  JSON Parsing

   The security considerations of [RFC8259] apply to the use of JSON as
   the data interchange format.

   As for any serialization format, parsers need to thoroughly check the
   syntax of the supplied data.  JSON uses opening and closing tags for
   several types and structures, and it is possible that the end of the
   supplied data will be reached when scanning for a matching closing
   tag; this is an error condition, and implementations need to stop
   scanning at the end of the supplied data.

   JSON also uses a string encoding with some escape sequences to encode
   special characters within a string.  Care is needed when processing
   these escape sequences to ensure that they are fully formed before
   the special processing is triggered, with special care taken when the
   escape sequences appear adjacent to other (non-escaped) special
   characters or adjacent to the end of data (as in the previous
   paragraph).

   If parsing JSON into a non-textual structured data format,
   implementations may need to allocate storage to hold JSON string
   elements.  Since JSON does not use explicit string lengths, the risk
   of denial of service due to resource exhaustion is small, but
   implementations may still wish to place limits on the size of
   allocations they are willing to make in any given context, to avoid
   untrusted data causing excessive memory allocation.

7.3.  URI Values

   Several JSCalendar properties contain URIs as values, and processing
   these properties requires extra care.  Section 7 of [RFC3986]
   discusses security risks related 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 often
   location) information.

   A maliciously constructed JSCalendar 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.

7.4.  Spam

   Calendar systems may receive JSCalendar files from untrusted sources,
   in particular, as attachments to emails.  This can be a vector for an
   attacker to inject spam into a user's calendar.  This may confuse,
   annoy, and mislead users or overwhelm their calendar with bogus
   events, preventing them from seeing legitimate ones.

   Heuristic, statistical, or machine-learning-based filters can be
   effective in filtering out spam.  Authentication mechanisms, such as
   DomainKeys Identified Mail (DKIM) [RFC6376], can help establish the
   source of messages and associate the data with existing relationships
   (such as an address book contact).  However, misclassifications are
   always possible and providing a mechanism for users to quickly
   correct this is advised.

   Confusable unicode characters may be used to trick a user into
   trusting a JSCalendar file that appears to come from a known contact
   but is actually from a similar-looking source controlled by an
   attacker.

7.5.  Duplication

   It is important for calendar systems to maintain the UID of an event
   when updating it to avoid an unexpected duplication of events.
   Consumers of the data may not remove the previous version of the
   event if it has a different UID.  This can lead to a confusing
   situation for the user, with many variations of the event and no
   indication of which one is correct.  Care must be taken by consumers
   of the data to remove old events where possible to avoid an
   accidental denial-of-service attack due to the volume of data.

7.6.  Time Zones

   Events recur in a particular time zone.  When this differs from the
   user's current time zone, it may unexpectedly cause an occurrence to
   shift in time for that user due to a daylight savings change in the
   event's time zone.  A maliciously crafted event could attempt to
   confuse users with such an event to ensure a meeting is missed.

8.  IANA Considerations

8.1.  Media Type Registration

   This document defines a media type for use with JSCalendar data
   formatted in JSON.

   Type name:  application

   Subtype name:  jscalendar+json

   Required parameters:  type

      The "type" parameter conveys the type of the JSCalendar data in
      the body part.  The allowed parameter values correspond to the
      "@type" property of the JSON-formatted JSCalendar object in the
      body:

      "event":  The "@type" property value MUST be "Event".

      "task":  The "@type" property value MUST be "Task".

      "group":  The "@type" property value MUST be "Group".

      No other parameter values are allowed.  The parameter MUST NOT
      occur more than once.

   Optional parameters:  none

   Encoding considerations:  This is the same as the encoding
      considerations of application/json, as specified in Section 11 of
      [RFC8259].

   Security considerations:  See Section 7 of this document.

   Interoperability considerations:  While JSCalendar is designed to
      avoid ambiguities as much as possible, when converting objects
      from other calendar formats to/from JSCalendar, it is possible
      that differing representations for the same logical data or
      ambiguities in interpretation might arise.  The semantic
      equivalence of two JSCalendar objects may be determined
      differently by different applications, for example, where URL
      values differ in case between the two objects.

   Published specification:  RFC 8984

   Applications that use this media type:  Applications that currently
      make use of the text/calendar and application/calendar+json media
      types can use this as an alternative.  Similarly, applications
      that use the application/json media type to transfer calendaring
      data can use this to further specify the content.

   Fragment identifier considerations:  A JSON Pointer fragment
      identifier may be used, as defined in [RFC6901], Section 6.

   Additional information:  Magic number(s):  N/A

                            File extensions(s):  N/A

                            Macintosh file type code(s):  N/A

   Person & email address to contact for further information:
      calsify@ietf.org

   Intended usage:  COMMON

   Restrictions on usage:  N/A

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

   Change controller:  IETF

8.2.  Creation of the "JSCalendar Properties" Registry

   IANA has created the "JSCalendar Properties" registry to allow
   interoperability of extensions to JSCalendar objects.

   This registry follows the Expert Review process ([RFC8126],
   Section 4.5).  If the "Intended Usage" field is "common", sufficient
   documentation is required to enable interoperability.  Preliminary
   community review for this registry is optional but strongly
   encouraged.

   A registration can have an intended usage of "common", "reserved", or
   "obsolete".  IANA will list registrations with a common usage
   designation prominently and separately from those with other intended
   usage values.

   A "reserved" registration reserves a property name without assigning
   semantics to avoid name collisions with future extensions or protocol
   use.

   An "obsolete" registration denotes a property that is no longer
   expected to be added by up-to-date systems.  A new property has
   probably been defined covering the obsolete property's semantics.

   The JSCalendar property registration procedure is not a formal
   standards process but rather an administrative procedure intended to
   allow community comment and check it is coherent without excessive
   time delay.  It is designed to encourage vendors to document and
   register new properties they add for use cases not covered by the
   original specification, leading to increased interoperability.

8.2.1.  Preliminary Community Review

   Notice of a potential new registration SHOULD be sent to the Calext
   mailing list <calsify@ietf.org> for review.  This mailing list is
   appropriate to solicit community feedback on a proposed new property.

   Property registrations must be marked with their intended use:
   "common", "reserved", or "obsolete".

   The intent of the public posting to this list is to solicit comments
   and feedback on the choice of the property name, the unambiguity of
   the specification document, and a review of any interoperability or
   security considerations.  The submitter may submit a revised
   registration proposal or abandon the registration completely at any
   time.

8.2.2.  Submit Request to IANA

   Registration requests can be sent to <iana@iana.org>.

8.2.3.  Designated Expert Review

   The primary concern of the designated expert (DE) is preventing name
   collisions and encouraging the submitter to document security and
   privacy considerations.  For a common-use registration, the DE is
   expected to confirm that suitable documentation, as described in
   Section 4.6 of [RFC8126], is available to ensure interoperability.
   That documentation will usually be in an RFC, but simple definitions
   are likely to use a web/wiki page, and if a sentence or two is deemed
   sufficient, it could be described in the registry itself.  The DE
   should also verify that the property name does not conflict with work
   that is active or already published within the IETF.  A published
   specification is not required for reserved or obsolete registrations.

   The DE will either approve or deny the registration request and
   publish a notice of the decision to the Calext WG mailing list or its
   successor, as well as inform IANA.  A denial notice must be justified
   by an explanation, and, in the cases where it is possible, concrete
   suggestions on how the request can be modified so as to become
   acceptable should be provided.

8.2.4.  Change Procedures

   Once a JSCalendar property has been published by IANA, the change
   controller may request a change to its definition.  The same
   procedure that would be appropriate for the original registration
   request is used to process a change request.

   JSCalendar property registrations may not be deleted; properties that
   are no longer believed appropriate for use can be declared obsolete
   by a change to their "intended usage" field; such properties will be
   clearly marked in the IANA registry.

   Significant changes to a JSCalendar property's definition should be
   requested only when there are serious omissions or errors in the
   published specification, as such changes may cause interoperability
   issues.  When review is required, a change request may be denied if
   it renders entities that were valid under the previous definition
   invalid under the new definition.

   The owner of a JSCalendar property may pass responsibility to another
   person or agency by informing IANA; this can be done without
   discussion or review.

8.2.5.  "JSCalendar Properties" Registry Template

   Property Name:  This is the name of the property.  The property name
      MUST NOT already be registered for any of the object types listed
      in the "Property Context" field of this registration.  Other
      object types MAY already have registered a different property with
      the same name; however, the same name SHOULD only be used when the
      semantics are analogous.

   Property Type:  This is the type of this property, using type
      signatures, as specified in Section 1.3.  The property type MUST
      be registered in the "JSCalendar Types" registry.

   Property Context:  This is a comma-separated list of JSCalendar
      object types this property is allowed on.

   Reference or Description:  This is a brief description or RFC number
      and section reference where the property is specified (omitted for
      "reserved" property names).

   Intended Usage:  This may be "common", "reserved", or "obsolete".

   Change Controller:  This is who may request a change to this entry's
      definition ("IETF" for RFCs from the IETF stream).

8.2.6.  Initial Contents for the "JSCalendar Properties" Registry

   The following table lists the initial entries of the "JSCalendar
   Properties" registry.  All properties are for common use.  All RFC
   section references are for this document.  The change controller for
   all these properties is "IETF".

   +====================+=================+================+===========+
   |Property Name       |Property Type    |Property Context|Reference  |
   |                    |                 |                |or         |
   |                    |                 |                |Description|
   +====================+=================+================+===========+
   |@type               |String           |Event, Task,    |Section    |
   |                    |                 |Group,          |4.1.1,     |
   |                    |                 |AbsoluteTrigger,|Section    |
   |                    |                 |Alert, Link,    |4.5.2,     |
   |                    |                 |Location, NDay, |Section    |
   |                    |                 |OffsetTrigger,  |1.4.11,    |
   |                    |                 |Participant,    |Section    |
   |                    |                 |RecurrenceRule, |4.2.5,     |
   |                    |                 |Relation,       |Section    |
   |                    |                 |TimeZone,       |4.4.6,     |
   |                    |                 |TimeZoneRule,   |Section    |
   |                    |                 |VirtualLocation |4.3.3,     |
   |                    |                 |                |Section    |
   |                    |                 |                |1.4.10,    |
   |                    |                 |                |Section    |
   |                    |                 |                |4.7.2,     |
   |                    |                 |                |Section    |
   |                    |                 |                |4.2.6      |
   +--------------------+-----------------+----------------+-----------+
   |acknowledged        |UTCDateTime      |Alert           |Section    |
   |                    |                 |                |4.5.2      |
   +--------------------+-----------------+----------------+-----------+
   |action              |String           |Alert           |Section    |
   |                    |                 |                |4.5.2      |
   +--------------------+-----------------+----------------+-----------+
   |alerts              |Id[Alert]        |Event, Task     |Section    |
   |                    |                 |                |4.5.2      |
   +--------------------+-----------------+----------------+-----------+
   |aliases             |String[Boolean]  |TimeZone        |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |byDay               |NDay[]           |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |byHour              |UnsignedInt[]    |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |byMinute            |UnsignedInt[]    |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |byMonth             |String[]         |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |byMonthDay          |Int[]            |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |bySecond            |UnsignedInt[]    |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |bySetPosition       |Int[]            |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |byWeekNo            |Int[]            |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |byYearDay           |Int[]            |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |categories          |String[Boolean]  |Event, Task,    |Section    |
   |                    |                 |Group           |4.2.10     |
   +--------------------+-----------------+----------------+-----------+
   |cid                 |String           |Link            |Section    |
   |                    |                 |                |1.4.11     |
   +--------------------+-----------------+----------------+-----------+
   |color               |String           |Event, Task,    |Section    |
   |                    |                 |Group           |4.2.11     |
   +--------------------+-----------------+----------------+-----------+
   |comments            |String[]         |TimeZoneRule    |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |contentType         |String           |Link            |Section    |
   |                    |                 |                |1.4.11     |
   +--------------------+-----------------+----------------+-----------+
   |coordinates         |String           |Location        |Section    |
   |                    |                 |                |4.2.5      |
   +--------------------+-----------------+----------------+-----------+
   |count               |UnsignedInt      |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |created             |UTCDateTime      |Event, Task,    |Section    |
   |                    |                 |Group           |4.1.5      |
   +--------------------+-----------------+----------------+-----------+
   |day                 |String           |NDay            |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |daylight            |TimeZoneRule[]   |TimeZone        |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |delegatedFrom       |Id[Boolean]      |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |delegatedTo         |Id[Boolean]      |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |description         |String           |Event, Task,    |Section    |
   |                    |                 |Location,       |4.2.2,     |
   |                    |                 |Participant,    |Section    |
   |                    |                 |VirtualLocation |4.2.5,     |
   |                    |                 |                |Section    |
   |                    |                 |                |4.4.6,     |
   |                    |                 |                |Section    |
   |                    |                 |                |4.2.6      |
   +--------------------+-----------------+----------------+-----------+
   |description         |String           |Event, Task     |Section    |
   |ContentType         |                 |                |4.2.3      |
   +--------------------+-----------------+----------------+-----------+
   |display             |String           |Link            |Section    |
   |                    |                 |                |1.4.11     |
   +--------------------+-----------------+----------------+-----------+
   |due                 |LocalDateTime    |Task            |Section    |
   |                    |                 |                |5.2.1      |
   +--------------------+-----------------+----------------+-----------+
   |duration            |Duration         |Event           |Section    |
   |                    |                 |                |5.1.2      |
   +--------------------+-----------------+----------------+-----------+
   |email               |String           |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |entries             |(Task|Event)[]   |Group           |Section    |
   |                    |                 |                |5.3.1      |
   +--------------------+-----------------+----------------+-----------+
   |estimatedDuration   |Duration         |Task            |Section    |
   |                    |                 |                |5.2.3      |
   +--------------------+-----------------+----------------+-----------+
   |excluded            |Boolean          |Event, Task     |Section    |
   |                    |                 |                |4.3.6      |
   +--------------------+-----------------+----------------+-----------+
   |excluded            |RecurrenceRule[] |Event, Task     |Section    |
   |RecurrenceRules     |                 |                |4.3.4      |
   +--------------------+-----------------+----------------+-----------+
   |expectReply         |Boolean          |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |features            |String[Boolean]  |VirtualLocation |Section    |
   |                    |                 |                |4.2.6      |
   +--------------------+-----------------+----------------+-----------+
   |firstDayOfWeek      |String           |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |freeBusyStatus      |String           |Event, Task     |Section    |
   |                    |                 |                |4.4.2      |
   +--------------------+-----------------+----------------+-----------+
   |frequency           |String           |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |href                |String           |Link            |Section    |
   |                    |                 |                |1.4.11     |
   +--------------------+-----------------+----------------+-----------+
   |interval            |UnsignedInt      |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |invitedBy           |Id               |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |keywords            |String[Boolean]  |Event, Task,    |Section    |
   |                    |                 |Group           |4.2.9      |
   +--------------------+-----------------+----------------+-----------+
   |kind                |String           |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |language            |String           |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |links               |Id[Link]         |Group, Event,   |Section    |
   |                    |                 |Task, Location, |4.2.7,     |
   |                    |                 |Participant     |Section    |
   |                    |                 |                |4.2.5,     |
   |                    |                 |                |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |locale              |String           |Group, Event,   |Section    |
   |                    |                 |Task            |4.2.8      |
   +--------------------+-----------------+----------------+-----------+
   |localizations       |String           |Event, Task     |Section    |
   |                    |[PatchObject]    |                |4.6.1      |
   +--------------------+-----------------+----------------+-----------+
   |locationId          |Id               |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |locations           |Id[Location]     |Event, Task     |Section    |
   |                    |                 |                |4.2.5      |
   +--------------------+-----------------+----------------+-----------+
   |locationTypes       |String[Boolean]  |Location        |Section    |
   |                    |                 |                |4.2.5      |
   +--------------------+-----------------+----------------+-----------+
   |memberOf            |Id[Boolean]      |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |method              |String           |Event, Task     |Section    |
   |                    |                 |                |4.1.8      |
   +--------------------+-----------------+----------------+-----------+
   |name                |String           |Location,       |Section    |
   |                    |                 |VirtualLocation,|4.2.5,     |
   |                    |                 |Participant     |Section    |
   |                    |                 |                |4.2.6,     |
   |                    |                 |                |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |names               |String[Boolean]  |TimeZoneRule    |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |nthOfPeriod         |Int              |NDay            |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |offset              |SignedDuration   |OffsetTrigger   |Section    |
   |                    |                 |                |4.5.2      |
   +--------------------+-----------------+----------------+-----------+
   |offsetFrom          |UTCDateTime      |TimeZoneRule    |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |offsetTo            |UTCDateTime      |TimeZoneRule    |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |participants        |Id[Participant]  |Event, Task     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |participationComment|String           |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |participationStatus |String           |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |percentComplete     |UnsignedInt      |Task,           |Section    |
   |                    |                 |Participant     |5.2.4      |
   +--------------------+-----------------+----------------+-----------+
   |priority            |Int              |Event, Task     |Section    |
   |                    |                 |                |4.4.1      |
   +--------------------+-----------------+----------------+-----------+
   |privacy             |String           |Event, Task     |Section    |
   |                    |                 |                |4.4.3      |
   +--------------------+-----------------+----------------+-----------+
   |prodId              |String           |Event, Task,    |Section    |
   |                    |                 |Group           |4.1.4      |
   +--------------------+-----------------+----------------+-----------+
   |progress            |String           |Task,           |Section    |
   |                    |                 |Participant     |5.2.5      |
   +--------------------+-----------------+----------------+-----------+
   |progressUpdated     |UTCDateTime      |Task,           |Section    |
   |                    |                 |Participant     |5.2.6      |
   +--------------------+-----------------+----------------+-----------+
   |recurrenceId        |LocalDateTime    |Event, Task     |Section    |
   |                    |                 |                |4.3.1      |
   +--------------------+-----------------+----------------+-----------+
   |recurrenceIdTimeZone|TimeZoneId|null  |Event, Task     |Section    |
   |                    |                 |                |4.3.2      |
   +--------------------+-----------------+----------------+-----------+
   |recurrenceOverrides |LocalDateTime    |Event, Task,    |Section    |
   |                    |[PatchObject]    |TimeZoneRule    |4.3.5,     |
   |                    |                 |                |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |recurrenceRules     |RecurrenceRule[] |Event, Task,    |Section    |
   |                    |                 |TimeZoneRule    |4.3.3,     |
   |                    |                 |                |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |rel                 |String           |Link            |Section    |
   |                    |                 |                |1.4.11     |
   +--------------------+-----------------+----------------+-----------+
   |relatedTo           |String[Relation] |Event, Task,    |Section    |
   |                    |                 |Alert           |4.1.3,     |
   |                    |                 |                |Section    |
   |                    |                 |                |4.5.2      |
   +--------------------+-----------------+----------------+-----------+
   |relation            |String[Boolean]  |Relation        |Section    |
   |                    |                 |                |1.4.10     |
   +--------------------+-----------------+----------------+-----------+
   |relativeTo          |String           |OffsetTrigger,  |Section    |
   |                    |                 |Location        |4.5.2,     |
   |                    |                 |                |Section    |
   |                    |                 |                |4.2.5      |
   +--------------------+-----------------+----------------+-----------+
   |replyTo             |String[String]   |Event, Task     |Section    |
   |                    |                 |                |4.4.4      |
   +--------------------+-----------------+----------------+-----------+
   |requestStatus       |String           |Event, Task     |Section    |
   |                    |                 |                |4.4.7      |
   +--------------------+-----------------+----------------+-----------+
   |roles               |String[Boolean]  |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |rscale              |String           |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |sentBy              |String           |Event, Task,    |Section    |
   |                    |                 |Participant     |4.4.5,     |
   |                    |                 |                |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |standard            |TimeZoneRule[]   |TimeZone        |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |start               |LocalDateTime    |TimeZoneRule    |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |scheduleAgent       |String           |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |scheduleForceSend   |Boolean          |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |scheduleSequence    |UnsignedInt      |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |scheduleStatus      |String[]         |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |scheduleUpdated     |UTCDateTime      |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |sendTo              |String[String]   |Participant     |Section    |
   |                    |                 |                |4.4.6      |
   +--------------------+-----------------+----------------+-----------+
   |sequence            |UnsignedInt      |Event, Task     |Section    |
   |                    |                 |                |4.1.7      |
   +--------------------+-----------------+----------------+-----------+
   |showWithoutTime     |Boolean          |Event, Task     |Section    |
   |                    |                 |                |4.2.4      |
   +--------------------+-----------------+----------------+-----------+
   |size                |UnsignedInt      |Link            |Section    |
   |                    |                 |                |1.4.11     |
   +--------------------+-----------------+----------------+-----------+
   |skip                |String           |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |source              |String           |Group           |Section    |
   |                    |                 |                |5.3.2      |
   +--------------------+-----------------+----------------+-----------+
   |start               |LocalDateTime    |Event, Task     |Section    |
   |                    |                 |                |5.1.1,     |
   |                    |                 |                |Section    |
   |                    |                 |                |5.2.2      |
   +--------------------+-----------------+----------------+-----------+
   |status              |String           |Event           |Section    |
   |                    |                 |                |5.1.3      |
   +--------------------+-----------------+----------------+-----------+
   |timeZone            |TimeZoneId|null  |Event, Task,    |Section    |
   |                    |                 |Location        |4.7.1,     |
   |                    |                 |                |Section    |
   |                    |                 |                |4.2.5      |
   +--------------------+-----------------+----------------+-----------+
   |timeZones           |TimeZoneId       |Event, Task     |Section    |
   |                    |[TimeZone]       |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |title               |String           |Event, Task,    |Section    |
   |                    |                 |Group, Link     |4.2.1      |
   +--------------------+-----------------+----------------+-----------+
   |trigger             |OffsetTrigger|   |Alert           |Section    |
   |                    |AbsoluteTrigger| |                |4.5.2      |
   |                    |UnknownTrigger   |                |           |
   +--------------------+-----------------+----------------+-----------+
   |tzId                |String           |TimeZone        |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |uid                 |String           |Event, Task,    |Section    |
   |                    |                 |Group           |4.1.2      |
   +--------------------+-----------------+----------------+-----------+
   |until               |LocalDateTime    |RecurrenceRule  |Section    |
   |                    |                 |                |4.3.3      |
   +--------------------+-----------------+----------------+-----------+
   |updated             |UTCDateTime      |Event, Task,    |Section    |
   |                    |                 |Group           |4.1.6      |
   +--------------------+-----------------+----------------+-----------+
   |uri                 |String           |VirtualLocation |Section    |
   |                    |                 |                |4.2.6      |
   +--------------------+-----------------+----------------+-----------+
   |url                 |String           |TimeZone        |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |useDefaultAlerts    |Boolean          |Event, Task     |Section    |
   |                    |                 |                |4.5.1      |
   +--------------------+-----------------+----------------+-----------+
   |validUntil          |UTCDateTime      |TimeZone        |Section    |
   |                    |                 |                |4.7.2      |
   +--------------------+-----------------+----------------+-----------+
   |virtualLocations    |Id               |Event, Task     |Section    |
   |                    |[VirtualLocation]|                |4.2.6      |
   +--------------------+-----------------+----------------+-----------+
   |when                |UTCDateTime      |AbsoluteTrigger |Section    |
   |                    |                 |                |4.5.2      |
   +--------------------+-----------------+----------------+-----------+

     Table 1: Initial Contents of the "JSCalendar Properties" Registry

8.3.  Creation of the "JSCalendar Types" Registry

   IANA has created the "JSCalendar Types" registry to avoid name
   collisions and provide a complete reference for all data types used
   for JSCalendar property values.  The registration process is the same
   as for the "JSCalendar Properties" registry, as defined in
   Section 8.2.

8.3.1.  "JSCalendar Types" Registry Template

   Type Name:  the name of the type

   Reference or Description:  a brief description or RFC number and
      section reference where the Type is specified (may be omitted for
      "reserved" type names)

   Intended Use:  common, reserved, or obsolete

   Change Controller:  who may request a change to this entry's
      definition ("IETF" for RFCs from the IETF stream)

8.3.2.  Initial Contents for the "JSCalendar Types" Registry

   The following table lists the initial entries of the JSCalendar Types
   registry.  All properties are for common use.  All RFC section
   references are for this document.  The change controller for all
   these properties is "IETF".

   +=================+==========================+
   | Type Name       | Reference or Description |
   +=================+==========================+
   | Alert           | Section 4.5.2            |
   +-----------------+--------------------------+
   | Boolean         | Section 1.3              |
   +-----------------+--------------------------+
   | Duration        | Section 1.4.6            |
   +-----------------+--------------------------+
   | Id              | Section 1.4.1            |
   +-----------------+--------------------------+
   | Int             | Section 1.4.2            |
   +-----------------+--------------------------+
   | LocalDateTime   | Section 1.4.5            |
   +-----------------+--------------------------+
   | Link            | Section 1.4.11           |
   +-----------------+--------------------------+
   | Location        | Section 4.2.5            |
   +-----------------+--------------------------+
   | NDay            | Section 4.3.3            |
   +-----------------+--------------------------+
   | Number          | Section 1.3              |
   +-----------------+--------------------------+
   | Participant     | Section 4.4.6            |
   +-----------------+--------------------------+
   | PatchObject     | Section 1.4.9            |
   +-----------------+--------------------------+
   | RecurrenceRule  | Section 4.3.3            |
   +-----------------+--------------------------+
   | Relation        | Section 1.4.10           |
   +-----------------+--------------------------+
   | SignedDuration  | Section 1.4.7            |
   +-----------------+--------------------------+
   | String          | Section 1.3              |
   +-----------------+--------------------------+
   | TimeZone        | Section 4.7.2            |
   +-----------------+--------------------------+
   | TimeZoneId      | Section 1.4.8            |
   +-----------------+--------------------------+
   | TimeZoneRule    | Section 4.7.2            |
   +-----------------+--------------------------+
   | UnsignedInt     | Section 1.4.3            |
   +-----------------+--------------------------+
   | UTCDateTime     | Section 1.4.4            |
   +-----------------+--------------------------+
   | VirtualLocation | Section 4.2.6            |
   +-----------------+--------------------------+

          Table 2: Initial Contents of the
            "JSCalendar Types" Registry

8.4.  Creation of the "JSCalendar Enum Values" Registry

   IANA has created the "JSCalendar Enum Values" registry to allow
   interoperable extension of semantics for properties with enumerable
   values.  Each such property will have a subregistry of allowed
   values.  The registration process for a new enum value or adding a
   new enumerable property is the same as for the "JSCalendar
   Properties" registry, as defined in Section 8.2.

8.4.1.  "JSCalendar Enum Values" Registry Property Template

   This template is for adding a subregistry for a new enumerable
   property to the "JSCalendar Enum" registry.

   Property Name:  These are the name(s) of the property or properties
      where these values may be used.  This MUST be registered in the
      "JSCalendar Properties" registry.

   Context:  This is the list of allowed object types where the property
      or properties may appear, as registered in the "JSCalendar
      Properties" registry.  This disambiguates where there may be two
      distinct properties with the same name in different contexts.

   Change Controller:  ("IETF" for properties defined in RFCs from the
      IETF stream).

   Initial Contents:  This is the initial list of defined values for
      this enum, using the template defined in Section 8.4.2.  A
      subregistry will be created with these values for this property
      name/context tuple.

8.4.2.  "JSCalendar Enum Values" Registry Value Template

   This template is for adding a new enum value to a subregistry in the
   JSCalendar Enum registry.

   Enum Value:  the verbatim value of the enum

   Reference or Description:  a brief description or RFC number and
      section reference for the semantics of this value

8.4.3.  Initial Contents for the "JSCalendar Enum Values" Registry

   For each subregistry created in this section, all RFC section
   references are for this document.

   Property Name:      action
   Context:            Alert
   Change Controller:  IETF
   Initial Contents:
                       +============+==========================+
                       | Enum Value | Reference or Description |
                       +============+==========================+
                       | display    | Section 4.5.2            |
                       +------------+--------------------------+
                       | email      | Section 4.5.2            |
                       +------------+--------------------------+

                          Table 3: JSCalendar Enum Values for
                                action (Context: Alert)

   Property Name:      display
   Context:            Link
   Change Controller:  IETF
   Initial Contents:
                       +============+==========================+
                       | Enum Value | Reference or Description |
                       +============+==========================+
                       | badge      | Section 1.4.11           |
                       +------------+--------------------------+
                       | graphic    | Section 1.4.11           |
                       +------------+--------------------------+
                       | fullsize   | Section 1.4.11           |
                       +------------+--------------------------+
                       | thumbnail  | Section 1.4.11           |
                       +------------+--------------------------+

                          Table 4: JSCalendar Enum Values for
                                display (Context: Link)

   Property Name:      features
   Context:            VirtualLocation
   Change Controller:  IETF
   Initial Contents:
                       +============+==========================+
                       | Enum Value | Reference or Description |
                       +============+==========================+
                       | audio      | Section 4.2.6            |
                       +------------+--------------------------+
                       | chat       | Section 4.2.6            |
                       +------------+--------------------------+
                       | feed       | Section 4.2.6            |
                       +------------+--------------------------+
                       | moderator  | Section 4.2.6            |
                       +------------+--------------------------+
                       | phone      | Section 4.2.6            |
                       +------------+--------------------------+
                       | screen     | Section 4.2.6            |
                       +------------+--------------------------+
                       | video      | Section 4.2.6            |
                       +------------+--------------------------+

                          Table 5: JSCalendar Enum Values for
                          features (Context: VirtualLocation)

   Property Name:      freeBusyStatus
   Context:            Event, Task
   Change Controller:  IETF
   Initial Contents:
                       +============+==========================+
                       | Enum Value | Reference or Description |
                       +============+==========================+
                       | free       | Section 4.4.2            |
                       +------------+--------------------------+
                       | busy       | Section 4.4.2            |
                       +------------+--------------------------+

                          Table 6: JSCalendar Enum Values for
                         freeBusyStatus (Context: Event, Task)

   Property Name:      kind
   Context:            Participant
   Change Controller:  IETF
   Initial Contents:
                       +============+==========================+
                       | Enum Value | Reference or Description |
                       +============+==========================+
                       | individual | Section 4.4.6            |
                       +------------+--------------------------+
                       | group      | Section 4.4.6            |
                       +------------+--------------------------+
                       | resource   | Section 4.4.6            |
                       +------------+--------------------------+
                       | location   | Section 4.4.6            |
                       +------------+--------------------------+

                          Table 7: JSCalendar Enum Values for
                              kind (Context: Participant)

   Property Name:      participationStatus
   Context:            Participant
   Change Controller:  IETF
   Initial Contents:
                       +==============+==========================+
                       | Enum Value   | Reference or Description |
                       +==============+==========================+
                       | needs-action | Section 4.4.6            |
                       +--------------+--------------------------+
                       | accepted     | Section 4.4.6            |
                       +--------------+--------------------------+
                       | declined     | Section 4.4.6            |
                       +--------------+--------------------------+
                       | tentative    | Section 4.4.6            |
                       +--------------+--------------------------+
                       | delegated    | Section 4.4.6            |
                       +--------------+--------------------------+

                           Table 8: JSCalendar Enum Values for
                              participationStatus (Context:
                                       Participant)

   Property Name:      privacy
   Context:            Event, Task
   Change Controller:  IETF
   Initial Contents:
                       +============+==========================+
                       | Enum Value | Reference or Description |
                       +============+==========================+
                       | public     | Section 4.4.3            |
                       +------------+--------------------------+
                       | private    | Section 4.4.3            |
                       +------------+--------------------------+
                       | secret     | Section 4.4.3            |
                       +------------+--------------------------+

                          Table 9: JSCalendar Enum Values for
                             privacy (Context: Event, Task)

   Property Name:      progress
   Context:            Task, Participant
   Change Controller:  IETF
   Initial Contents:
                       +==============+==========================+
                       | Enum Value   | Reference or Description |
                       +==============+==========================+
                       | needs-action | Section 5.2.5            |
                       +--------------+--------------------------+
                       | in-process   | Section 5.2.5            |
                       +--------------+--------------------------+
                       | completed    | Section 5.2.5            |
                       +--------------+--------------------------+
                       | failed       | Section 5.2.5            |
                       +--------------+--------------------------+
                       | cancelled    | Section 5.2.5            |
                       +--------------+--------------------------+

                           Table 10: JSCalendar Enum Values for
                          progress (Context: Task, Participant)

   Property Name:      relation
   Context:            Relation
   Change Controller:  IETF
   Initial Contents:
                       +============+==========================+
                       | Enum Value | Reference or Description |
                       +============+==========================+
                       | first      | Section 1.4.10           |
                       +------------+--------------------------+
                       | next       | Section 1.4.10           |
                       +------------+--------------------------+
                       | child      | Section 1.4.10           |
                       +------------+--------------------------+
                       | parent     | Section 1.4.10           |
                       +------------+--------------------------+

                          Table 11: JSCalendar Enum Values for
                              relation (Context: Relation)

   Property Name:      relativeTo
   Context:            OffsetTrigger, Location
   Change Controller:  IETF
   Initial Contents:
                       +============+==========================+
                       | Enum Value | Reference or Description |
                       +============+==========================+
                       | start      | Section 4.5.2            |
                       +------------+--------------------------+
                       | end        | Section 4.5.2            |
                       +------------+--------------------------+

                          Table 12: JSCalendar Enum Values for
                          relativeTo (Context: OffsetTrigger,
                                       Location)

   Property Name:      roles
   Context:            Participant
   Change Controller:  IETF
   Initial Contents:
                       +===============+==========================+
                       | Enum Value    | Reference or Description |
                       +===============+==========================+
                       | owner         | Section 4.4.6            |
                       +---------------+--------------------------+
                       | attendee      | Section 4.4.6            |
                       +---------------+--------------------------+
                       | optional      | Section 4.4.6            |
                       +---------------+--------------------------+
                       | informational | Section 4.4.6            |
                       +---------------+--------------------------+
                       | chair         | Section 4.4.6            |
                       +---------------+--------------------------+
                       | contact       | Section 4.4.6            |
                       +---------------+--------------------------+

                           Table 13: JSCalendar Enum Values for
                               roles (Context: Participant)

   Property Name:      scheduleAgent
   Context:            Participant
   Change Controller:  IETF
   Initial Contents:
                       +============+==========================+
                       | Enum Value | Reference or Description |
                       +============+==========================+
                       | server     | Section 4.4.6            |
                       +------------+--------------------------+
                       | client     | Section 4.4.6            |
                       +------------+--------------------------+
                       | none       | Section 4.4.6            |
                       +------------+--------------------------+

                          Table 14: JSCalendar Enum Values for
                          scheduleAgent (Context: Participant)

   Property Name:      status
   Context:            Event
   Change Controller:  IETF
   Initial Contents:
                       +============+==========================+
                       | Enum Value | Reference or Description |
                       +============+==========================+
                       | confirmed  | Section 5.1.3            |
                       +------------+--------------------------+
                       | cancelled  | Section 5.1.3            |
                       +------------+--------------------------+
                       | tentative  | Section 5.1.3            |
                       +------------+--------------------------+

                          Table 15: JSCalendar Enum Values for
                                status (Context: Event)

9.  References

9.1.  Normative References

   [CLDR]     "Unicode Common Locale Data Repository",
              <http://cldr.unicode.org/>.

   [COLORS]   Çelik, T., Lilley, C., and L. Baron, "CSS Color Module
              Level 3", W3C Recommendation, June 2018,
              <https://www.w3.org/TR/css-color-3/>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC2392]  Levinson, E., "Content-ID and Message-ID Uniform Resource
              Locators", RFC 2392, DOI 10.17487/RFC2392, August 1998,
              <https://www.rfc-editor.org/info/rfc2392>.

   [RFC2397]  Masinter, L., "The "data" URL scheme", RFC 2397,
              DOI 10.17487/RFC2397, August 1998,
              <https://www.rfc-editor.org/info/rfc2397>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <https://www.rfc-editor.org/info/rfc3339>.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [RFC4122]  Leach, P., Mealling, M., and R. Salz, "A Universally
              Unique IDentifier (UUID) URN Namespace", RFC 4122,
              DOI 10.17487/RFC4122, July 2005,
              <https://www.rfc-editor.org/info/rfc4122>.

   [RFC4589]  Schulzrinne, H. and H. Tschofenig, "Location Types
              Registry", RFC 4589, DOI 10.17487/RFC4589, July 2006,
              <https://www.rfc-editor.org/info/rfc4589>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC5322]  Resnick, P., Ed., "Internet Message Format", RFC 5322,
              DOI 10.17487/RFC5322, October 2008,
              <https://www.rfc-editor.org/info/rfc5322>.

   [RFC5545]  Desruisseaux, B., Ed., "Internet Calendaring and
              Scheduling Core Object Specification (iCalendar)",
              RFC 5545, DOI 10.17487/RFC5545, September 2009,
              <https://www.rfc-editor.org/info/rfc5545>.

   [RFC5546]  Daboo, C., Ed., "iCalendar Transport-Independent
              Interoperability Protocol (iTIP)", RFC 5546,
              DOI 10.17487/RFC5546, December 2009,
              <https://www.rfc-editor.org/info/rfc5546>.

   [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
              Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
              September 2009, <https://www.rfc-editor.org/info/rfc5646>.

   [RFC5870]  Mayrhofer, A. and C. Spanring, "A Uniform Resource
              Identifier for Geographic Locations ('geo' URI)",
              RFC 5870, DOI 10.17487/RFC5870, June 2010,
              <https://www.rfc-editor.org/info/rfc5870>.

   [RFC6047]  Melnikov, A., Ed., "iCalendar Message-Based
              Interoperability Protocol (iMIP)", RFC 6047,
              DOI 10.17487/RFC6047, December 2010,
              <https://www.rfc-editor.org/info/rfc6047>.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13,
              RFC 6838, DOI 10.17487/RFC6838, January 2013,
              <https://www.rfc-editor.org/info/rfc6838>.

   [RFC6901]  Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,
              <https://www.rfc-editor.org/info/rfc6901>.

   [RFC7493]  Bray, T., Ed., "The I-JSON Message Format", RFC 7493,
              DOI 10.17487/RFC7493, March 2015,
              <https://www.rfc-editor.org/info/rfc7493>.

   [RFC7529]  Daboo, C. and G. Yakushev, "Non-Gregorian Recurrence Rules
              in the Internet Calendaring and Scheduling Core Object
              Specification (iCalendar)", RFC 7529,
              DOI 10.17487/RFC7529, May 2015,
              <https://www.rfc-editor.org/info/rfc7529>.

   [RFC7808]  Douglass, M. and C. Daboo, "Time Zone Data Distribution
              Service", RFC 7808, DOI 10.17487/RFC7808, March 2016,
              <https://www.rfc-editor.org/info/rfc7808>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8288]  Nottingham, M., "Web Linking", RFC 8288,
              DOI 10.17487/RFC8288, October 2017,
              <https://www.rfc-editor.org/info/rfc8288>.

   [TZDB]     IANA, "Time Zone Database",
              <https://www.iana.org/time-zones>.

9.2.  Informative References

   [ISO.9070.1991]
              ISO/IEC, "Information technology -- SGML support
              facilities -- Registration procedures for public text
              owner identifiers", Edition 2, ISO/IEC 9070:1991, April
              1991, <https://www.iso.org/standard/16645.html>.

   [LINKRELS] IANA, "Link Relations: Link Relation Types",
              <https://www.iana.org/assignments/link-relations>.

   [LOCATIONTYPES]
              IANA, "Location Types Registry",
              <https://www.iana.org/assignments/location-type-registry>.

   [MEDIATYPES]
              IANA, "Media Types",
              <https://www.iana.org/assignments/media-types>.

   [RFC6376]  Crocker, D., Ed., Hansen, T., Ed., and M. Kucherawy, Ed.,
              "DomainKeys Identified Mail (DKIM) Signatures", STD 76,
              RFC 6376, DOI 10.17487/RFC6376, September 2011,
              <https://www.rfc-editor.org/info/rfc6376>.

   [RFC7265]  Kewisch, P., Daboo, C., and M. Douglass, "jCal: The JSON
              Format for iCalendar", RFC 7265, DOI 10.17487/RFC7265, May
              2014, <https://www.rfc-editor.org/info/rfc7265>.

   [RFC7986]  Daboo, C., "New Properties for iCalendar", RFC 7986,
              DOI 10.17487/RFC7986, October 2016,
              <https://www.rfc-editor.org/info/rfc7986>.

Acknowledgments

   The authors would like to thank the members of CalConnect for their
   valuable contributions.  This specification originated from the work
   of the API technical committee of CalConnect: The Calendaring and
   Scheduling Consortium.

Authors' Addresses

   Neil Jenkins
   Fastmail
   Collins St. West
   P.O. Box 234
   Melbourne  VIC 8007
   Australia

   Email: neilj@fastmailteam.com
   URI:   https://www.fastmail.com


   Robert Stepanek
   Fastmail
   Collins St. West
   P.O. Box 234
   Melbourne  VIC 8007
   Australia

   Email: rsto@fastmailteam.com
   URI:   https://www.fastmail.com