JSCalendar: A JSON representation of calendar data

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 modelled 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 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 I-JSON format , which is a strict subset of the JavaScript Object Notation (JSON) Data Interchange Format . 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.

The iCalendar data format , a widely deployed interchange format for calendaring and scheduling data, has served calendaring vendors for a long while, but contains some ambiguities and pitfalls that can not be overcome without backward-incompatible changes. Sources of implementation errors include the following: iCalendar defines various formats for local times, UTC time, 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 understandings 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, 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 timezone'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.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. 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 . Some examples in this document contain "partial" JSON documents used for illustrative purposes. In these examples, three periods "..." are used to indicate a portion of the document that has been removed for compactness.

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 - The JSON string type. Number - The JSON number type. Boolean - The JSON boolean type. A[B] - A JSON object where the keys are all of type A, and the values are all of type B. A[] - 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, with their representations defined elsewhere in this document.

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

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 , 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 JSEvent objects might use the same Ids in their respective links properties. Or within the same JSEvent object the same Id could appear in the participants and alerts properties. These situations do not imply any semantic connections among the objects. Nevertheless, a UUID is typically a good choice.

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.

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.

This is a string in date-time 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.

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 ). 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 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) and 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 ), 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.

Where Duration is given as a type, it means a length of time represented by a subset of ISO8601 duration format, as specified by the following ABNF :

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: Add any week or day components of the duration to the date. A week is always the same as 7 days. If a time zone applies to the LocalDateTime, convert it to a UTCDateTime following the semantics in . Add any hour, minute or second components of the duration (in absolute time). 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: If a time zone applies to the LocalDateTime, convert it to UTC following the semantics in . Subtract any hour, minute or second components of the duration (in absolute time). Convert the resulting UTCDateTime back to LocalDateTime in the time zone that applies. Subtract any week or day components of the duration from the date. If the resulting time does not exist on the date due to a discontinuity in the time zone, use the semantics in to convert to UTC and back to get a valid LocalDateTime. These semantics match the iCalendar DURATION value type (, Section 3.3.6).

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:

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

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 or a custom time zone identifier defined in the timeZones property (see ). Where an IANA time zone is specified, the zone rules of the respective zone records apply. Custom time zones are interpreted as described in .

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 JSON pointer format . 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: 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). All parts prior to the last (i.e., the value after the final slash) MUST already exist on the object being patched. 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. 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. Anything else: The value to set 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 ). A @type property in a patch MUST be handled as any other patched property value. Implementations MUST reject in its entirety a PatchObject if any of its patches is 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.

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) Specifies the type of this object. This MUST be Relation. relation: String[Boolean] (optional, default: empty Object) 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, or specified in the property definition where the Relation object is used, or a value registered in the IANA JSCalendar Enum Values registry, or a vendor-specific value (see ): first: The linked object is the first in a series the linking object is part of. next: The linked object is the 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.

A Link object represents an external resource associated with the linking object. It has the following properties: @type: String (mandatory) Specifies the type of this object. This MUST be Link. href: String (mandatory) A URI from which the resource may be fetched. This MAY be a data: URL , 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 in . 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) The media type of the resource, if known. size: UnsignedInt (optional) 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) Identifies the relation of the linked resource to the object. If set, the value MUST be a relation type from the IANA registry , as established in . display: String (optional) 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 ): 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) A human-readable plain-text description of the resource.

This section describes the calendar object types specified by JSCalendar.

Media type: application/jscalendar+json;type=jsevent A JSEvent 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 property value MUST be jsevent.

Media type: application/jscalendar+json;type=jstask A JSTask represents an action-item, assignment, to-do or work item. It may start and be due at certain points in time, may take some estimated time to complete, and may recur, none of which is required. The @type property value MUST be jstask.

Media type: application/jscalendar+json;type=jsgroup A JSGroup is a collection of JSEvent and/or JSTask objects. Typically, objects are grouped by topic (e.g., by keywords) or calendar membership. The @type property value MUST be jsgroup.

A JSCalendar object is a JSON object , which MUST be valid I-JSON (a stricter subset of JSON) . 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.

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.

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 ). 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.

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 a @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.

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 describe the set of supported properties per type.

Type: String (mandatory). Specifies the type which this object represents. This MUST be one of the following values: jsevent: a JSCalendar event (). jstask: a JSCalendar task (). jsgroup: a JSCalendar group ().

Type: String (mandatory). A globally unique identifier, used to associate the object as the same across different systems, calendars and views. The value of this property MUST be unique across all JSCalendar objects, even if they are of different type. describes a range of established algorithms to generate universally unique identifiers (UUID). UUID version 4, described in Section 4.4 of , is RECOMMENDED. For compatibility with UIDs, 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.

Type: String[Relation] (optional). 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 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.

Type: String (optional). 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 an 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 non-standard properties, a practice that is known to cause long-term interoperability problems.

Type: UTCDateTime (optional). The date and time this object was initially created.

Type: UTCDateTime (mandatory). The date and time the data in this object was last modified (or its creation date/time if not modified since).

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 ). This is used as part of iTIP to know which version of the object a scheduling message relates to.

Type: String (optional). The iTIP method, in lowercase. This MUST only be present if the JSCalendar object represents an iTIP scheduling message.

Type: String (optional, default: empty String). A short summary of the object.

Type: String (optional, default: empty String). A longer-form text description of the object. The content is formatted according to the descriptionContentType property.

Type: String (optional, default: text/plain). Describes the media type of the contents of the description property. Media types MUST be sub-types of type text, and SHOULD be text/plain or text/html . They MAY include parameters and the charset parameter value MUST be utf-8, if specified. Descriptions of type text/html MAY contain cid URLs to reference links in the calendar object by use of the cid property of the Link object.

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

Type: Id[Location] (optional). 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) Specifies the type of this object. This MUST be Location. name: String (optional) The human-readable name of the location. description: String (optional) 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) A set of one or more location types that describe this location. All types MUST be from the Location Types Registry as defined in . 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) 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 ). 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) A time zone for this location. coordinates: String (optional) A geo: URI for the location. links: Id[Link] (optional) 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).

Type: Id[VirtualLocation] (optional). 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) Specifies the type of this object. This MUST be VirtualLocation. name: String (optional, default: empty String) The human-readable name of the virtual location. description: String (optional) Human-readable plain-text instructions for accessing this virtual location. This may be a conference access code, etc. uri: String (mandatory) A URI 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.

Type: Id[Link] (optional). 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 as attachments for download. Links with a rel of describedby MUST be considered by the client to be an alternative representation of the description. Links with a rel of icon MUST be considered by the client to be an image 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.

Type: String (optional). The language tag as defined in that best describes the locale used for the text in the calendar object, if known.

Type: String[Boolean] (optional). 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.

Type: String[Boolean] (optional). 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 typically are 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.

Type: String (optional). 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 , or an RGB value in hexadecimal notation, as defined in Section 4.2.1 of CSS Color Module Level 3.

Some events and tasks occur at regular or irregular intervals. Rather than having to copy the data for every occurrence there can be a master 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: The recurrenceRules property () generates a set of extra date-times on which the object occurs. The excludedRecurrenceRules property () generates a set of date-times that are to be removed from the previously generated set of date-times on which the object occurs. The recurrenceOverrides property () defines date-times which are added or excluded to form the final set. (This property may also contain changes to the object to apply to particular instances.)

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 master event, or added as a key to the recurrenceOverrides property of the master event.

Type: RecurrenceRule[] (optional). Defines a set of recurrence rules (repeating patterns) for recurring calendar objects. A JSEvent recurs by applying the recurrence rules to the start date-time. A JSTask 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 used, ignoring any duplicates. A RecurrenceRule object is a JSON object mapping of a RECUR value type in iCalendar and has the same semantics. It has the following properties: @type: String (mandatory) Specifies the type of this object. This MUST be RecurrenceRule. frequency: String (mandatory) The time span covered by each iteration of this recurrence rule (see 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) 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") The calendar system in which this recurrence rule operates, in lowercase. This MUST be either a CLDR-registered calendar system name , or a vendor-specific value (see ). This is the RSCALE part from iCalendar RSCALE, converted to lowercase. skip: String (optional, default: "omit") The behaviour 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, converted to lowercase. firstDayOfWeek: String (optional, default: "mo") The day on which the week is considered to start, represented as a lowercase abbreviated 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) Days of the week on which to repeat. An NDay object has the following properties: @type: String (mandatory) Specifies the type of this object. This MUST be NDay. day: String (mandatory) 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 nth-last of period. This is the ordinal part of the BYDAY value in iCalendar (e.g., 1 or -3). byMonthDay: Int[] (optional) 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) 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 ) 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) 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) 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) 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) 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) 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) 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) 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) 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: 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.

A recurrence rule specifies a set of date-times for recurring calendar objects. A recurrence rule has the following semantics. Note, 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. 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 1st day of a year (inclusive) to midnight the 1st 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 1st day of a month (inclusive) to midnight on the 1st 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 7 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: the second itself, only. 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 means 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., 31st February in the Gregorian calendar). In this case, the properties MUST be considered in the order above and: 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. 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"). If any valid date produced after applying the skip is already a candidate, eliminate the duplicate. (For example after adjusting, 30th February and 31st February would both become the same "real" date, so one is eliminated as a duplicate.) 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 indexes from the end of the list, with -1 being the last item. Any date-times before the start date of the event are eliminated (see below for why this might be needed). 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".) 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: The initial date-time to which the rule is applied (the start date-time for events; 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. 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) as outlined before. The following properties MUST be implicitly added to the rule under the given conditions: If frequency is not secondly and 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 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 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 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 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 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 is 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.

Type: RecurrenceRule[] (optional). 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 ), with the exception that the initial date-time to which the rule is applied (the "start" date-time for events; 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 are then removed from those generated by the recurrenceRules property, as described in .

Type: LocalDateTime[PatchObject] (optional). A map of the recurrence ids (the date-time produced by the recurrence rule) to an object of patches to apply to the generated occurrence object. 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 recurrenceOverrides recurrenceRules relatedTo replyTo uid

Type: Boolean (optional, default: false). Defines if this object is an overridden, excluded instance of a recurring JSCalendar object (see ). 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 false, indicates that this instance MUST be included in the occurrence expansion.

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

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

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 are 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 ). 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 is shared. The following properties MAY be shared, any other properties MUST NOT be shared: @type created due duration estimatedDuration freeBusyStatus privacy recurrenceOverrides. Only patches which 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.

Type: String[String] (optional). 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 iMIP 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.

Type: Id[Participant] (optional). 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) Specifies the type of this object. This MUST be Participant. name: String (optional) The display name of the participant (e.g., "Joe Bloggs"). email: String (optional) The email address for the participant. description: String (optional). 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) 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 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) 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 ). 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) 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 ): owner: The participant is an owner of the object. This signifies they have permission to make changes to it that affect the other participants. Non-owner participants may only change properties that just affect 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: String (optional) 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) The language tag as defined in that best describes the participant's preferred language, if known. participationStatus: String (optional, default: needs-action) 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 ): needs-action: No status yet 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) 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) 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 ): 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) The sequence number of the last response from the participant. If defined, this MUST be a non-negative 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) A list of status codes, as defined in Section 3.8.8.3 of , returned from the processing of the most recent scheduling message sent to this participant. 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) 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. invitedBy: String (optional) The participant id of the participant who invited this one, if known. delegatedTo: String[Boolean] (optional) A 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: String[Boolean] (optional) 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: String[Boolean] (optional) 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) 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 JSTask). 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 for allowed values and semantics. progressUpdated: UTCDateTime (optional; only allowed for participants of a JSTask). Specifies the date-time the progress property was last set on this participant. See for allowed values and semantics. percentComplete: UnsignedInt (optional; only allowed for participants of a JSTask). Represents the percent completion of the participant for this task. The property value MUST be a positive integer between 0 and 100.

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.

Type: Id[Alert] (optional). 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) Specifies the type of this object. This MUST be Alert. trigger: OffsetTrigger|AbsoluteTrigger|UnknownTrigger (mandatory) Defines when to trigger the alert. New types may be defined in future documents. An OffsetTrigger object has the following properties: @type: String (mandatory) Specifies the type of this object. This MUST be OffsetTrigger. offset: SignedDuration (mandatory). 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. relativeTo: String (optional, default: start) Specifies the time property that the alert offset is relative to. The value MUST be one of: 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) Specifies the type of this object. This MUST be AbsoluteTrigger. when: UTCDateTime (mandatory). Defines a specific UTC date-time when the alert is triggered. An UnknownTrigger object is an object that contains a @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 master 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 successfully carried out. relatedTo: String[Relation] (optional) 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) 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 ): 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 about the alert. This action is typically only appropriate for server implementations.

Type: String[PatchObject] (optional). A map of language tags to patch objects, which localize the calendar object into the locale of the respective language tag. See the description of PatchObject 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.

Type: TimeZoneId|null (optional, default: null). Identifies the time zone the object is scheduled in, or null for floating time. This is either a name from the IANA Time Zone Database or the TimeZoneId of a custom time zone from the timeZones property (). If omitted, this MUST be presumed to be null (i.e., floating time).

Type: TimeZoneId[TimeZone] (optional). 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 , it MUST start with the / character. It MUST be a valid paramtext value as specified in Section 3.1. of . 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. A JSCalendar object may be part in a hierarchy of other JSCalendar objects (say, a JSEvent is an entry in a JSGroup). 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 JSEvent, a time zone definition in its timeZones property has precedence over a definition of the same id in the JSGroup). 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 there. A valid time zone MUST define at least one transition rule in the standard or daylight property. Its properties are: @type: String (mandatory) Specifies the type of this object. This MUST be TimeZone. tzId: String (mandatory). The TZID property from iCalendar. updated: UTCDateTime (optional) The LAST-MODIFIED property from iCalendar. url: String (optional) The TZURL property from iCalendar. validUntil: UTCDateTime (optional) The TZUNTIL property from iCalendar specified in . aliases: String[Boolean] (optional) Maps the TZID-ALIAS-OF properties from iCalendar specified in 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) The STANDARD sub-components from iCalendar. The order MUST be preserved during conversion. daylight: TimeZoneRule[] (optional). 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) Specifies the type of this object. This MUST be TimeZoneRule. start: LocalDateTime (mandatory) The DTSTART property from iCalendar. offsetFrom: String (mandatory) The TZOFFSETFROM property from iCalendar. offsetTo: String (mandatory) The TZOFFSETTO property from iCalendar. recurrenceRules: RecurrenceRule[] (optional) The RRULE property mapped as specified in . During recurrence rule evaluation, the until property value MUST be interpreted as a local time in the UTC time zone. recurrenceOverrides: LocalDateTime[PatchObject] (optional) 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) 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). Maps the COMMENT properties from iCalendar. The order MUST be preserved during conversion.

In addition to the common JSCalendar object properties a JSEvent has the following properties:

Type: LocalDateTime (mandatory). The date/time the event starts in the event's time zone (as specified in the timeZone property, see ).

Type: Duration (optional, default: PT0S). 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. A JSEvent MAY involve start and end locations that are in different time zones (e.g., a trans-continental flight). This can be expressed using the relativeTo and timeZone properties of the JSEvent's Location objects (see ).

Type: String (optional, default: confirmed). The scheduling status () of a JSEvent. 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 ): confirmed: Indicates the event is definitely happening. cancelled: Indicates the event has been cancelled. tentative: Indicates the event may happen.

In addition to the common JSCalendar object properties a JSTask has the following properties:

Type: LocalDateTime (optional). The date/time the task is due in the task's time zone.

Type: LocalDateTime (optional). The date/time the task should start in the task's time zone.

Type: Duration (optional). Specifies the estimated positive duration of time the task takes to complete.

Type: UnsignedInt (optional). Represents the percent completion of the task overall. The property value MUST be a positive integer between 0 and 100.

Type: String (optional). Defines the progress of this task. If omitted, the default progress () of a JSTask 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 ): 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.

Type: UTCDateTime (optional). Specifies the date/time the progress property of either the task overall () or a specific participant () 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 JSTask into a current, single instance of JSTask with this instance progress update time and a future recurring instance. See also on splitting.

JSGroup supports the following common JSCalendar properties: @type uid prodId created updated title description descriptionContentType links locale keywords categories color timeZones In addition, the following JSGroup-specific properties are supported:

Type: (JSTask|JSEvent)[] (mandatory). A collection of group members. Implementations MUST ignore entries of unknown type.

Type: String (optional). The source from which updated versions of this group may be retrieved from. The value MUST be a URI.

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.

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

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

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

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.

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

This example illustrates the use of end time zones by use of an international flight. The flight starts on April 1, 2020 at 9am 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.

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

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.

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 9am 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 10am. Also, the location of the exam differs from the usual location. On April 1 no course is held. On January 7 at 2pm is an optional introduction course, that occurs before the first regular lecture.

This example illustrates scheduled events. A team meeting occurs every week since January 8, 2020 at 9am 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.

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 the patterns of behavior of the user in both the physical and cyber realm. Additionally, calendar events and tasks can could 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 organiser 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 just defines the data format; such considerations are primarily the concern of the API or method of storage and transmission of such files.

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, 9am 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.

The Security Considerations of 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.

Several JSCalendar properties contain URIs as values, and processing these properties requires extra care. Section 7 of 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 generally 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.

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 DKIM can help establish the source of messages and associate the data with existing relationships (such as an address book contact). Misclassifications are always possible, however, 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.

It is important for calendar systems to maintain the UID of an event when updating it to avoid 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.

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.

This document defines a media type for use with JSCalendar data formatted in JSON. application jscalendar+json type The type parameter conveys the type of the JSCalendar data in the body part, with the value being one of jsevent, jstask, or jsgroup. The parameter MUST NOT occur more than once. It MUST match the value of the @type property of the JSON-formatted JSCalendar object in the body. none Same as encoding considerations of application/json as specified in RFC8529, Section 11. See of this document. 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 might arise, or ambiguities in interpretation. 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. This specification. 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. A JSON Pointer fragment identifier may be used, as defined in , Section 6. N/A N/A N/A calsify@ietf.org COMMON N/A See the "Author's Address" section of this document. IETF

The IANA will create the "JSCalendar Properties" registry to allow interoperability of extensions to JSCalendar objects. This registry follows the Expert Review process (, Section 4.5). If the "intended use" 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 use of common, reserved, or obsolete. The IANA will list common-use registrations prominently and separately from those with other intended use 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 sanity checking 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.

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. Properties 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.

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

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 , 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.

Once a JSCalendar property has been published by the 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 use" field; such properties will be clearly marked in the lists published by the IANA. 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 the IANA; this can be done without discussion or review.

Property Name: 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: The type of this property, using type signatures as specified in . The property type MUST be registed in the Type Registry. Property Context: A comma-separated list of JSCalendar object types this property is allowed on. Reference or Description: A brief description or RFC number and section reference where the property is specified (omitted for "reserved" property names). Intended Use: Common, reserved, or obsolete. Change Controller: Who may request a change to this entry's definition (IETF for IETF-stream RFCs).

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 JSEvent, JSTask, JSGroup, AbsoluteTrigger, Alert, Link, Location, NDay, OffsetTrigger, Participant, RecurrenceRule, Relation, TimeZone, TimeZoneRule, VirtualLocation , , , , , , , , , acknowledged UTCDateTime Alert action String Alert alerts Id[Alert] JSEvent, JSTask aliases String[Boolean] TimeZone byDay NDay[] RecurrenceRule byHour UnsignedInt[] RecurrenceRule byMinute UnsignedInt[] RecurrenceRule byMonth String[] RecurrenceRule byMonthDay Int[] RecurrenceRule bySecond UnsignedInt[] RecurrenceRule bySetPosition Int[] RecurrenceRule byWeekNo Int[] RecurrenceRule byYearDay Int[] RecurrenceRule categories String[Boolean] JSEvent, JSTask, JSGroup cid String Link color String JSEvent, JSTask, JSGroup comments String[] TimeZoneRule contentType String Link coordinates String Location count UnsignedInt RecurrenceRule created UTCDateTime JSEvent, JSTask, JSGroup day String NDay daylight TimeZoneRule TimeZone delegatedFrom String[Boolean] Participant delegatedTo String[Boolean] Participant description String JSEvent, JSTask, Location, Participant, VirtualLocation , , , descriptionContentType String JSEvent, JSTask display String Link due LocalDateTime JSTask duration Duration JSEvent email String Participant entries (JSTask|JSEvent)[] JSGroup estimatedDuration Duration JSTask excluded Boolean JSEvent, JSTask excludedRecurrenceRules RecurrenceRule[] JSEvent, JSTask expectReply Boolean Participant firstDayOfWeek String RecurrenceRule freeBusyStatus String JSEvent, JSTask frequency String RecurrenceRule href String Link interval UnsignedInt RecurrenceRule invitedBy String Participant keywords String[Boolean] JSEvent, JSTask, JSGroup kind String Participant language String Participant links Id[Link] JSGroup, JSEvent, JSTask, Location, Participant , , locale String JSGroup, JSEvent, JSTask localizations String[PatchObject] JSEvent, JSTask locationId String Participant locations Id[Location] JSEvent, JSTask locationTypes String[Boolean] Location memberOf String[Boolean] Participant method String JSEvent, JSTask name String Location, VirtualLocation, Participant , , names String[Boolean] TimeZoneRule nthOfPeriod Int NDay offset SignedDuration OffsetTrigger offsetFrom UTCDateTime TimeZoneRule offsetTo UTCDateTime TimeZoneRule participants Id[Participant] JSEvent, JSTask participationComment String Participant participationStatus String Participant percentComplete UnsignedInt JSTask, Participant priority Int JSEvent, JSTask privacy String JSEvent, JSTask prodId String JSEvent, JSTask, JSGroup progress String JSTask, Participant progressUpdated UTCDateTime JSTask, Participant recurrenceId LocalDateTime JSEvent, JSTask recurrenceOverrides LocalDateTime[PatchObject] JSEvent, JSTask, TimeZoneRule , recurrenceRules RecurrenceRule[] JSEvent, JSTask, TimeZoneRule , rel String Link relatedTo String[Relation] JSEvent, JSTask, Alert , relation String[Boolean] Relation relativeTo String OffsetTrigger, Location , replyTo String[String] JSEvent, JSTask roles String[Boolean] Participant rscale String RecurrenceRule standard TimeZoneRule TimeZone start LocalDateTime TimeZoneRule scheduleAgent String Participant scheduleForceSend Boolean Participant scheduleSequence UnsignedInt Participant scheduleStatus String[] Participant scheduleUpdated UTCDateTime Participant sendTo String[String] Participant sequence UnsignedInt JSEvent, JSTask showWithoutTime Boolean JSEvent, JSTask size UnsignedInt Link skip String RecurrenceRule source String JSGroup start LocalDateTime JSEvent, JSTask , status String JSEvent timeZone TimeZoneId|null JSEvent, JSTask, Location , timeZones TimeZoneId[TimeZone] JSEvent, JSTask title String JSEvent, JSTask, JSGroup, Link trigger OffsetTrigger|AbsoluteTrigger|UnknownTrigger Alert tzId String TimeZone uid String JSEvent, JSTask, JSGroup until LocalDateTime RecurrenceRule updated UTCDateTime JSEvent, JSTask, JSGroup uri String VirtualLocation url String TimeZone useDefaultAlerts Boolean JSEvent, JSTask validUntil UTCDateTime TimeZone virtualLocations Id[VirtualLocation] JSEvent, JSTask when UTCDateTime AbsoluteTrigger

The IANA will create 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 .

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 IETF-stream RFCs).

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 Boolean Duration Id Int LocalDateTime Link Location NDay Number Participant PatchObject RecurrenceRule Relation SignedDuration String TimeZone TimeZoneId TimeZoneRule UnsignedInt UTCDateTime VirtualLocation

The IANA will create 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 .

This template is for adding a subregistry for a new enumerable property to the JSCalendar Enum registry. Property Name: the name(s) of the property or properties where these values may be used. This MUST be registered in the JSCalendar Properties registry. Context: 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 IETF-stream RFCs). Initial Contents: The initial list of defined values for this enum, using the template defined in . A subregistry will be created with these values for this property name/context tuple.

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.

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 email ------------------------------------------------------------ Property Name: display Context: Link Change Controller: IETF Initial Contents: Enum Value Reference or Description badge graphic fullsize thumbnail ------------------------------------------------------------ Property Name: freeBusyStatus Context: JSEvent, JSTask Change Controller: IETF Initial Contents: Enum Value Reference or Description free busy ------------------------------------------------------------ Property Name: kind Context: Participant Change Controller: IETF Initial Contents: Enum Value Reference or Description individual group resource location ------------------------------------------------------------ Property Name: participationStatus Context: Participant Change Controller: IETF Initial Contents: Enum Value Reference or Description needs-action accepted declined tenative delegated ------------------------------------------------------------ Property Name: privacy Context: JSEvent, JSTask Change Controller: IETF Initial Contents: Enum Value Reference or Description public private secret ------------------------------------------------------------ Property Name: progress Context: JSTask, Participant Change Controller: IETF Initial Contents: Enum Value Reference or Description needs-action in-process completed failed cancelled ------------------------------------------------------------ Property Name: relation Context: Relation Change Controller: IETF Initial Contents: Enum Value Reference or Description first next child parent ------------------------------------------------------------ Property Name: relativeTo Context: OffsetTrigger, Location Change Controller: IETF Initial Contents: Enum Value Reference or Description start end ------------------------------------------------------------ Property Name: roles Context: Participant Change Controller: IETF Initial Contents: Enum Value Reference or Description owner attendee optional informational chair contact ------------------------------------------------------------ Property Name: scheduleAgent Context: Participant Change Controller: IETF Initial Contents: Enum Value Reference or Description server client none ------------------------------------------------------------ Property Name: status Context: JSEvent Change Controller: IETF Initial Contents: Enum Value Reference or Description confirmed cancelled tentative

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.