Network Working Group B. Desruisseaux, Ed. Internet-Draft Oracle Obsoletes: 2445 (if approved) March 2, 2007 Intended status: Standards Track Expires: September 3, 2007 Internet Calendaring and Scheduling Core Object Specification (iCalendar) draft-ietf-calsify-rfc2445bis-06 Status of This Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 3, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document defines a MIME media type for representing and exchanging calendaring and scheduling information such as events, to- dos, journal entries and free/busy information. The definition of the text/calendar media type, known as iCalendar, is independent of any particular calendar service or protocol. Desruisseaux Expires September 3, 2007 [Page 1] Internet-Draft iCalendar March 2007 Editorial Note (To be removed by RFC Editor prior to publication) This document is a product of the Calendaring and Scheduling Standards Simplification (Calsify) working group of the Internet Engineering Task Force. Comments on this draft are welcomed, and should be addressed to the ietf-calsify@osafoundation.org [1] mailing list. The issues raised on this mailing list are being tracked at the following web site: http://www.ofcourseimright.com/cgi-bin/roundup/calsify. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Basic Grammar and Conventions . . . . . . . . . . . . . . . . 7 2.1. Formatting Conventions . . . . . . . . . . . . . . . . . 7 2.2. Related Memos . . . . . . . . . . . . . . . . . . . . . . 8 2.3. International Considerations . . . . . . . . . . . . . . 8 3. iCalendar Object Specification . . . . . . . . . . . . . . . 9 3.1. Content Lines . . . . . . . . . . . . . . . . . . . . . . 9 3.1.1. List and Field Separators . . . . . . . . . . . . . . 11 3.1.2. Multiple Values . . . . . . . . . . . . . . . . . . . 12 3.1.3. Binary Content . . . . . . . . . . . . . . . . . . . 12 3.1.4. Character Set . . . . . . . . . . . . . . . . . . . . 13 3.2. Property Parameters . . . . . . . . . . . . . . . . . . . 13 3.2.1. Alternate Text Representation . . . . . . . . . . . . 14 3.2.2. Common Name . . . . . . . . . . . . . . . . . . . . . 15 3.2.3. Calendar User Type . . . . . . . . . . . . . . . . . 16 3.2.4. Delegators . . . . . . . . . . . . . . . . . . . . . 16 3.2.5. Delegatees . . . . . . . . . . . . . . . . . . . . . 17 3.2.6. Directory Entry Reference . . . . . . . . . . . . . . 17 3.2.7. Inline Encoding . . . . . . . . . . . . . . . . . . . 18 3.2.8. Format Type . . . . . . . . . . . . . . . . . . . . . 19 3.2.9. Free/Busy Time Type . . . . . . . . . . . . . . . . . 19 3.2.10. Language . . . . . . . . . . . . . . . . . . . . . . 20 3.2.11. Group or List Membership . . . . . . . . . . . . . . 21 3.2.12. Participation Status . . . . . . . . . . . . . . . . 21 3.2.13. Alarm Trigger Relationship . . . . . . . . . . . . . 23 3.2.14. Relationship Type . . . . . . . . . . . . . . . . . . 23 3.2.15. Participation Role . . . . . . . . . . . . . . . . . 24 3.2.16. RSVP Expectation . . . . . . . . . . . . . . . . . . 25 3.2.17. Sent By . . . . . . . . . . . . . . . . . . . . . . . 25 3.2.18. Time Zone Identifier . . . . . . . . . . . . . . . . 26 3.2.19. Value Data Types . . . . . . . . . . . . . . . . . . 27 3.3. Property Value Data Types . . . . . . . . . . . . . . . . 28 3.3.1. Binary . . . . . . . . . . . . . . . . . . . . . . . 28 3.3.2. Boolean . . . . . . . . . . . . . . . . . . . . . . . 29 3.3.3. Calendar User Address . . . . . . . . . . . . . . . . 30 3.3.4. Date . . . . . . . . . . . . . . . . . . . . . . . . 30 Desruisseaux Expires September 3, 2007 [Page 2] Internet-Draft iCalendar March 2007 3.3.5. Date-Time . . . . . . . . . . . . . . . . . . . . . . 31 3.3.6. Duration . . . . . . . . . . . . . . . . . . . . . . 33 3.3.7. Float . . . . . . . . . . . . . . . . . . . . . . . . 34 3.3.8. Integer . . . . . . . . . . . . . . . . . . . . . . . 35 3.3.9. Period of Time . . . . . . . . . . . . . . . . . . . 35 3.3.10. Recurrence Rule . . . . . . . . . . . . . . . . . . . 36 3.3.11. Text . . . . . . . . . . . . . . . . . . . . . . . . 42 3.3.12. Time . . . . . . . . . . . . . . . . . . . . . . . . 43 3.3.13. URI . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.3.14. UTC Offset . . . . . . . . . . . . . . . . . . . . . 46 3.4. iCalendar Object . . . . . . . . . . . . . . . . . . . . 47 3.5. Property . . . . . . . . . . . . . . . . . . . . . . . . 47 3.6. Calendar Components . . . . . . . . . . . . . . . . . . . 48 3.6.1. Event Component . . . . . . . . . . . . . . . . . . . 49 3.6.2. To-do Component . . . . . . . . . . . . . . . . . . . 52 3.6.3. Journal Component . . . . . . . . . . . . . . . . . . 54 3.6.4. Free/Busy Component . . . . . . . . . . . . . . . . . 56 3.6.5. Time Zone Component . . . . . . . . . . . . . . . . . 59 3.6.6. Alarm Component . . . . . . . . . . . . . . . . . . . 68 3.7. Calendar Properties . . . . . . . . . . . . . . . . . . . 74 3.7.1. Calendar Scale . . . . . . . . . . . . . . . . . . . 74 3.7.2. Method . . . . . . . . . . . . . . . . . . . . . . . 74 3.7.3. Product Identifier . . . . . . . . . . . . . . . . . 75 3.7.4. Version . . . . . . . . . . . . . . . . . . . . . . . 76 3.8. Component Properties . . . . . . . . . . . . . . . . . . 77 3.8.1. Descriptive Component Properties . . . . . . . . . . 77 3.8.1.1. Attachment . . . . . . . . . . . . . . . . . . . 77 3.8.1.2. Categories . . . . . . . . . . . . . . . . . . . 79 3.8.1.3. Classification . . . . . . . . . . . . . . . . . 80 3.8.1.4. Comment . . . . . . . . . . . . . . . . . . . . . 81 3.8.1.5. Description . . . . . . . . . . . . . . . . . . . 82 3.8.1.6. Geographic Position . . . . . . . . . . . . . . . 83 3.8.1.7. Location . . . . . . . . . . . . . . . . . . . . 84 3.8.1.8. Percent Complete . . . . . . . . . . . . . . . . 86 3.8.1.9. Priority . . . . . . . . . . . . . . . . . . . . 86 3.8.1.10. Resources . . . . . . . . . . . . . . . . . . . . 88 3.8.1.11. Status . . . . . . . . . . . . . . . . . . . . . 89 3.8.1.12. Summary . . . . . . . . . . . . . . . . . . . . . 91 3.8.2. Date and Time Component Properties . . . . . . . . . 92 3.8.2.1. Date/Time Completed . . . . . . . . . . . . . . . 92 3.8.2.2. Date/Time End . . . . . . . . . . . . . . . . . . 92 3.8.2.3. Date/Time Due . . . . . . . . . . . . . . . . . . 93 3.8.2.4. Date/Time Start . . . . . . . . . . . . . . . . . 95 3.8.2.5. Duration . . . . . . . . . . . . . . . . . . . . 96 3.8.2.6. Free/Busy Time . . . . . . . . . . . . . . . . . 97 3.8.2.7. Time Transparency . . . . . . . . . . . . . . . . 98 3.8.3. Time Zone Component Properties . . . . . . . . . . . 99 3.8.3.1. Time Zone Identifier . . . . . . . . . . . . . . 99 Desruisseaux Expires September 3, 2007 [Page 3] Internet-Draft iCalendar March 2007 3.8.3.2. Time Zone Name . . . . . . . . . . . . . . . . . 101 3.8.3.3. Time Zone Offset From . . . . . . . . . . . . . . 102 3.8.3.4. Time Zone Offset To . . . . . . . . . . . . . . . 102 3.8.3.5. Time Zone URL . . . . . . . . . . . . . . . . . . 103 3.8.4. Relationship Component Properties . . . . . . . . . . 104 3.8.4.1. Attendee . . . . . . . . . . . . . . . . . . . . 104 3.8.4.2. Contact . . . . . . . . . . . . . . . . . . . . . 107 3.8.4.3. Organizer . . . . . . . . . . . . . . . . . . . . 108 3.8.4.4. Recurrence ID . . . . . . . . . . . . . . . . . . 110 3.8.4.5. Related To . . . . . . . . . . . . . . . . . . . 112 3.8.4.6. Uniform Resource Locator . . . . . . . . . . . . 114 3.8.4.7. Unique Identifier . . . . . . . . . . . . . . . . 114 3.8.5. Recurrence Component Properties . . . . . . . . . . . 116 3.8.5.1. Exception Date/Times . . . . . . . . . . . . . . 116 3.8.5.2. Recurrence Date/Times . . . . . . . . . . . . . . 118 3.8.5.3. Recurrence Rule . . . . . . . . . . . . . . . . . 119 3.8.6. Alarm Component Properties . . . . . . . . . . . . . 130 3.8.6.1. Action . . . . . . . . . . . . . . . . . . . . . 130 3.8.6.2. Repeat Count . . . . . . . . . . . . . . . . . . 130 3.8.6.3. Trigger . . . . . . . . . . . . . . . . . . . . . 131 3.8.7. Change Management Component Properties . . . . . . . 134 3.8.7.1. Date/Time Created . . . . . . . . . . . . . . . . 134 3.8.7.2. Date/Time Stamp . . . . . . . . . . . . . . . . . 134 3.8.7.3. Last Modified . . . . . . . . . . . . . . . . . . 135 3.8.7.4. Sequence Number . . . . . . . . . . . . . . . . . 136 3.8.8. Miscellaneous Component Properties . . . . . . . . . 138 3.8.8.1. IANA Properties . . . . . . . . . . . . . . . . . 138 3.8.8.2. Non-standard Properties . . . . . . . . . . . . . 138 3.8.8.3. Request Status . . . . . . . . . . . . . . . . . 139 4. iCalendar Object Examples . . . . . . . . . . . . . . . . . . 143 5. Recommended Practices . . . . . . . . . . . . . . . . . . . . 147 6. Registration of Content Type Elements . . . . . . . . . . . . 148 6.1. Registration of New and Modified iCalendar Object Methods . . . . . . . . . . . . . . . . . . . . . . . . . 148 6.2. Registration of New Properties . . . . . . . . . . . . . 148 6.2.1. Define the property . . . . . . . . . . . . . . . . . 149 6.2.2. Post the Property definition . . . . . . . . . . . . 150 6.2.3. Allow a comment period . . . . . . . . . . . . . . . 150 6.2.4. Submit the property for approval . . . . . . . . . . 150 6.3. Property Change Control . . . . . . . . . . . . . . . . . 151 7. Internationalization Considerations . . . . . . . . . . . . . 151 8. Security Considerations . . . . . . . . . . . . . . . . . . . 151 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 152 9.1. Components Registry . . . . . . . . . . . . . . . . . . . 152 9.2. Properties Registry . . . . . . . . . . . . . . . . . . . 153 9.3. Property Parameters Registry . . . . . . . . . . . . . . 154 9.4. Value Data Type Values Registry . . . . . . . . . . . . . 155 9.5. Calendar User Type Values Registry . . . . . . . . . . . 156 Desruisseaux Expires September 3, 2007 [Page 4] Internet-Draft iCalendar March 2007 9.6. Free/Busy Time Type Values Registry . . . . . . . . . . . 156 9.7. Participation Status Values Registry . . . . . . . . . . 157 9.8. Relationship Type Values Registry . . . . . . . . . . . . 157 9.9. Participation Role Values Registry . . . . . . . . . . . 158 9.10. Action Values Registry . . . . . . . . . . . . . . . . . 158 9.11. Method Values Registry . . . . . . . . . . . . . . . . . 158 9.12. Media Type Registration Information . . . . . . . . . . . 158 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 161 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 162 11.1. Normative References . . . . . . . . . . . . . . . . . . 162 11.2. Informative References . . . . . . . . . . . . . . . . . 163 Appendix A. Differences from RFC 2445 . . . . . . . . . . . . . 164 A.1. New restrictions . . . . . . . . . . . . . . . . . . . . 164 A.2. Deprecated features . . . . . . . . . . . . . . . . . . . 165 Appendix B. Change Log (to be removed by RFC Editor prior to publication) . . . . . . . . . . . . . . . . . . . . 165 B.1. Changes in -06 . . . . . . . . . . . . . . . . . . . . . 165 B.2. Changes in -05 . . . . . . . . . . . . . . . . . . . . . 166 B.3. Changes in -04 . . . . . . . . . . . . . . . . . . . . . 167 B.4. Changes in -03 . . . . . . . . . . . . . . . . . . . . . 169 B.5. Changes in -02 . . . . . . . . . . . . . . . . . . . . . 169 B.6. Changes in -01 . . . . . . . . . . . . . . . . . . . . . 170 Appendix C. Open issues (to be removed by RFC Editor prior to publication) . . . . . . . . . . . . . . . . . . . . 170 C.1. update_intro . . . . . . . . . . . . . . . . . . . . . . 170 C.2. update_vtimezone_examples . . . . . . . . . . . . . . . . 170 C.3. #issue10+end_date_not_inclusive . . . . . . . . . . . . . 171 C.4. #issue61+ianaparam . . . . . . . . . . . . . . . . . . . 171 C.5. #issue11+4.3.10_byxxx_rule_part_examples . . . . . . . . 171 C.6. #issue75+4.6.5_rdate_format_in_vtimezone . . . . . . . . 171 C.7. #issue79+4.6.5_dtstart_and_rdate_in_vtimezone . . . . . . 172 C.8. 4.8.1.1_attach_description_incomplete . . . . . . . . . . 172 C.9. 4.8.1.4_comment_description_incomplete . . . . . . . . . 172 C.10. 4.8.2.1_completed_description_incomplete . . . . . . . . 172 C.11. #issue76+4.8.2.2_dtend_dtstart_value_type . . . . . . . . 172 C.12. #issue77+4.8.2.3_due_dtstart_value_type . . . . . . . . . 173 C.13. 4.8.2.3_due_description_incomplete . . . . . . . . . . . 173 C.14. #issue63+4.8.5.3_rdate_and_dtstart . . . . . . . . . . . 173 C.15. 4.8.6.2_repeat_description_incomplete . . . . . . . . . . 173 C.16. 4.8.7.1_created_description_incomplete . . . . . . . . . 174 C.17. 4.8.7.2_dtstamp_description_incomplete . . . . . . . . . 174 C.18. #issue65+6_recommended_practices_tzid . . . . . . . . . . 174 C.19. add_i18n_section . . . . . . . . . . . . . . . . . . . . 174 C.20. #issue19+iana_considerations . . . . . . . . . . . . . . 174 Desruisseaux Expires September 3, 2007 [Page 5] Internet-Draft iCalendar March 2007 1. Introduction The use of calendaring and scheduling has grown considerably in the last decade. Enterprise and inter-enterprise business has become dependent on rapid scheduling of events and actions using this information technology. However, the longer term growth of calendaring and scheduling is currently limited by the lack of Internet standards for the message content types that are central to these knowledgeware applications. This memo is intended to progress the level of interoperability possible between dissimilar calendaring and scheduling applications. This memo defines a MIME content type for exchanging electronic calendaring and scheduling information. The Internet Calendaring and Scheduling Core Object Specification, or iCalendar, allows for the capture and exchange of information normally stored within a calendaring and scheduling application; such as a Personal Information Manager (PIM) or a Group Scheduling product. The iCalendar format is suitable as an exchange format between applications or systems. The format is defined in terms of a MIME content type. This will enable the object to be exchanged using several transports, including but not limited to SMTP, HTTP, a file system, desktop interactive protocols such as the use of a memory- based clipboard or drag/drop interactions, point-to-point asynchronous communication, wired-network transport, or some form of unwired transport such as infrared might also be used. The memo also provides for the definition of iCalendar object methods that will map this content type to a set of messages for supporting calendaring and scheduling operations such as requesting, replying to, modifying, and canceling meetings or appointments, to-dos and journal entries. The iCalendar object methods can be used to define other calendaring and scheduling operations such a requesting for and replying with free/busy time data. Such a scheduling protocol is defined in the iCalendar Transport-independent Interoperability Protocol (iTIP) defined in [I-D.ietf-calsify-2446bis]. The memo also includes a formal grammar for the content type based on the Internet ABNF defined in [RFC4234]. This ABNF is required for the implementation of parsers and to serve as the definitive reference when ambiguities or questions arise in interpreting the descriptive prose definition of the memo. Additional restrictions that could not easily be expressed with the ABNF syntax are specified as comments in the ABNF. Comments with normative statements should be treated as such. Desruisseaux Expires September 3, 2007 [Page 6] Internet-Draft iCalendar March 2007 2. Basic Grammar and Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY" and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. This memo makes use of both a descriptive prose and a more formal notation for defining the calendaring and scheduling format. The notation used in this memo is the ABNF notation of [RFC4234]. Readers intending on implementing the format defined in this memo should be familiar with this notation in order to properly interpret the specifications of this memo. All numeric values used in this memo are given in decimal notation. All names of properties, property parameters, enumerated property values and property parameter values are case-insensitive. However, all other property values are case-sensitive, unless otherwise stated. Note: All indented editorial notes, such as this one, are intended to provide the reader with additional information. The information is not essential to the building of an implementation conformant with this memo. The information is provided to highlight a particular feature or characteristic of the memo. The format for the iCalendar object is based on the syntax of the text/directory media type [RFC2425]. While the iCalendar object is not a profile of the text/directory media type [RFC2425], it does reuse a number of the elements from the [RFC2425] specification. 2.1. Formatting Conventions The elements defined in this memo are defined in prose. Many of the terms used to describe these have common usage that is different than the standards usage of this memo. In order to reference within this memo elements of the calendaring and scheduling model, core object (this memo) or interoperability protocol [I-D.ietf-calsify-2446bis] some formatting conventions have been used. Calendaring and scheduling roles are referred to in quoted-strings of text with the first character of each word in upper case. For example, "Organizer" refers to a role of a "Calendar User" within the scheduling protocol defined by [I-D.ietf-calsify-2446bis]. Calendar components defined by this memo are referred to with capitalized, quoted-strings of text. All calendar components start with the letter "V". For example, "VEVENT" refers to the event calendar component, "VTODO" Desruisseaux Expires September 3, 2007 [Page 7] Internet-Draft iCalendar March 2007 refers to the to-do calendar component and "VJOURNAL" refers to the daily journal calendar component. Scheduling methods defined by iTIP [I-D.ietf-calsify-2446bis] are referred to with capitalized, quoted- strings of text. For example, "REQUEST" refers to the method for requesting a scheduling calendar component be created or modified, "REPLY" refers to the method a recipient of a request uses to update their status with the "Organizer" of the calendar component. The properties defined by this memo are referred to with capitalized, quoted-strings of text, followed by the word "property". For example, "ATTENDEE" property refers to the iCalendar property used to convey the calendar address of a calendar user. Property parameters defined by this memo are referred to with lowercase, quoted-strings of text, followed by the word "parameter". For example, "value" parameter refers to the iCalendar property parameter used to override the default value type for a property value. Enumerated values defined by this memo are referred to with capitalized text, either alone or followed by the word "value". For example, the "MINUTELY" value can be used with the "FREQ" component of the "RECUR" value type to specify repeating components based on an interval of one minute or more. 2.2. Related Memos Implementers will need to be familiar with several other memos that, along with this memo, form a framework for Internet calendaring and scheduling standards. This memo specifies a core specification of objects, value types, properties and property parameters. o iTIP [I-D.ietf-calsify-2446bis] specifies an interoperability protocol for scheduling between different implementations; o iMIP [I-D.ietf-calsify-rfc2447bis] specifies an Internet email binding for [I-D.ietf-calsify-2446bis]. This memo does not attempt to repeat the specification of concepts or definitions from these other memos. Where possible, references are made to the memo that provides for the specification of these concepts or definitions. 2.3. International Considerations In the rest of this document, descriptions of characters are of the form "character name (codepoint)", where "codepoint" is from the US- ASCII character set. The "character name" is the authoritative description; (codepoint) is a reference to that character in US- ASCII. Desruisseaux Expires September 3, 2007 [Page 8] Internet-Draft iCalendar March 2007 3. iCalendar Object Specification The following sections define the details of a Calendaring and Scheduling Core Object Specification. This information is intended to be an integral part of the MIME content type registration. In addition, this information can be used independent of such content registration. In particular, this memo has direct applicability for use as a calendaring and scheduling exchange format in file-, memory- or network-based transport mechanisms. 3.1. Content Lines The iCalendar object is organized into individual lines of text, called content lines. Content lines are delimited by a line break, which is a CRLF sequence (US-ASCII decimal 13, followed by US-ASCII decimal 10). Lines of text SHOULD NOT be longer than 75 octets, excluding the line break. Long content lines SHOULD be split into a multiple line representations using a line "folding" technique. That is, a long line can be split between any two characters by inserting a CRLF immediately followed by a single linear white space character (i.e., SPACE, US-ASCII decimal 32 or HTAB, US-ASCII decimal 9). Any sequence of CRLF followed immediately by a single linear white space character is ignored (i.e., removed) when processing the content type. For example the line: DESCRIPTION:This is a long description that exists on a long line. Can be represented as: DESCRIPTION:This is a lo ng description that exists on a long line. The process of moving from this folded multiple line representation to its single line representation is called "unfolding". Unfolding is accomplished by removing the CRLF character and the linear white space character that immediately follows. When parsing a content line, folded lines MUST first be unfolded according to the unfolding procedure described above. Note: It is possible for very simple implementations to generate improperly folded lines in the middle of a UTF-8 multi-octet sequence. For this reason, implementations need to unfold lines Desruisseaux Expires September 3, 2007 [Page 9] Internet-Draft iCalendar March 2007 in such a way to properly restore the original sequence. The content information associated with an iCalendar object is formatted using a syntax similar to that defined by [RFC2425]. That is, the content information consists of CRLF-separated content lines. The following notation defines the lines of content in an iCalendar object: contentline = name *(";" param ) ":" value CRLF ; This ABNF is just a general definition for an initial parsing ; of the content line into its property name, parameter list, ; and value string ; When parsing a content line, folded lines MUST first ; be unfolded according to the unfolding procedure ; described above. When generating a content line, lines ; longer than 75 octets SHOULD be folded according to ; the folding procedure described above. name = iana-token / x-name iana-token = 1*(ALPHA / DIGIT / "-") ; iCalendar identifier registered with IANA x-name = "X-" [vendorid "-"] 1*(ALPHA / DIGIT / "-") ; Reserved for experimental use. vendorid = 3*(ALPHA / DIGIT) ; Vendor identification param = param-name "=" param-value *("," param-value) ; Each property defines the specific ABNF for the parameters ; allowed on the property. Refer to specific properties for ; precise parameter ABNF. param-name = iana-token / x-name param-value = paramtext / quoted-string paramtext = *SAFE-CHAR value = *VALUE-CHAR quoted-string = DQUOTE *QSAFE-CHAR DQUOTE QSAFE-CHAR = WSP / %x21 / %x23-7E / NON-US-ASCII ; Any character except CONTROL and DQUOTE Desruisseaux Expires September 3, 2007 [Page 10] Internet-Draft iCalendar March 2007 SAFE-CHAR = WSP / %x21 / %x23-2B / %x2D-39 / %x3C-7E / NON-US-ASCII ; Any character except CONTROL, DQUOTE, ";", ":", "," VALUE-CHAR = WSP / %x21-7E / NON-US-ASCII ; Any textual character NON-US-ASCII = UTF8-2 / UTF8-3 / UTF8-4 ; UTF8-2, UTF8-3, and UTF8-4 are defined in [RFC3629] CONTROL = %x00-08 / %x0A-1F / %x7F ; All the controls except HTAB The property value component of a content line has a format that is property specific. Refer to the section describing each property for a definition of this format. All names of properties, property parameters, enumerated property values and property parameter values are case-insensitive. However, all other property values are case-sensitive, unless otherwise stated. 3.1.1. List and Field Separators Some properties and parameters allow a list of values. Values in a list of values MUST be separated by a COMMA character (US-ASCII decimal 44). There is no significance to the order of values in a list. For those parameter values (such as those that specify URI values) that are specified in quoted-strings, the individual quoted- strings are separated by a COMMA character (US-ASCII decimal 44). Some property values are defined in terms of multiple parts. These structured property values MUST have their value parts separated by a SEMICOLON character (US-ASCII decimal 59). Some properties allow a list of parameters. Each property parameter in a list of property parameters MUST be separated by a SEMICOLON character (US-ASCII decimal 59). Property parameters with values containing a COLON character (US- ASCII decimal 58), a SEMICOLON character (US-ASCII decimal 59) or a COMMA character (US-ASCII decimal 44) MUST be placed in quoted text. For example, in the following properties a SEMICOLON is used to separate property parameters from each other, and a COMMA is used to separate property values in a value list. Desruisseaux Expires September 3, 2007 [Page 11] Internet-Draft iCalendar March 2007 ATTENDEE;RSVP=TRUE;ROLE=REQ-PARTICIPANT:mailto: jsmith@example.com RDATE;VALUE=DATE:19970304,19970504,19970704,19970904 3.1.2. Multiple Values Some properties defined in the iCalendar object can have multiple values. The general rule for encoding multi-valued items is to simply create a new content line for each value, including the property name. However, it should be noted that some properties support encoding multiple values in a single property by separating the values with a COMMA character (US-ASCII decimal 44). Individual property definitions should be consulted for determining whether a specific property allows multiple values and in which of these two forms. 3.1.3. Binary Content Binary content information in an iCalendar object SHOULD be referenced using a URI within a property value. That is the binary content information SHOULD be placed in an external MIME entity that can be referenced by a URI from within the iCalendar object. In applications where this is not feasible, binary content information can be included within an iCalendar object, but only after first encoding it into text using the "BASE64" encoding method defined in [RFC4648]. Inline binary content SHOULD only be used in applications whose special circumstances demand that an iCalendar object be expressed as a single entity. A property containing inline binary content information MUST specify the "ENCODING" property parameter. Binary content information placed external to the iCalendar object MUST be referenced by a uniform resource identifier (URI). The following example specifies an "ATTACH" property that references an attachment external to the iCalendar object with a URI reference: ATTACH:http://example.com/public/quarterly-report.doc The following example specifies an "ATTACH" property with inline binary encoded content information: ATTACH;FMTTYPE=image/basic;ENCODING=BASE64;VALUE=BINARY: MIICajCCAdOgAwIBAgICBEUwDQYJKoZIhvcNAQEEBQAwdzELMAkGA1U EBhMCVVMxLDAqBgNVBAoTI05ldHNjYXBlIENvbW11bmljYXRpb25zIE <...remainder of "BASE64" encoded binary data...> Desruisseaux Expires September 3, 2007 [Page 12] Internet-Draft iCalendar March 2007 3.1.4. Character Set There is not a property parameter to declare the charset used in a property value. The default charset for an iCalendar stream is UTF-8 as defined in [RFC3629]. The "charset" Content-Type parameter MUST be used in MIME transports to specify the charset being used. 3.2. Property Parameters A property can have attributes associated with it. These "property parameters" contain meta-information about the property or the property value. Property parameters are provided to specify such information as the location of an alternate text representation for a property value, the language of a text property value, the value type of the property value and other attributes. Property parameter values that contain the COLON (US-ASCII decimal 58), SEMICOLON (US-ASCII decimal 59) or COMMA (US-ASCII decimal 44) character separators MUST be specified as quoted-string text values. Property parameter values MUST NOT contain the DQUOTE (US-ASCII decimal 22) character. The DQUOTE (US-ASCII decimal 22) character is used as a delimiter for parameter values that contain restricted characters or URI text. For example: DESCRIPTION;ALTREP="http://www.example.org":The Fall'98 Wild Wizards Conference - - Las Vegas\, NV\, USA Property parameter values that are not in quoted strings are case insensitive. The general property parameters defined by this memo are defined by the following notation: Desruisseaux Expires September 3, 2007 [Page 13] Internet-Draft iCalendar March 2007 icalparameter = altrepparam ; Alternate text representation / cnparam ; Common name / cutypeparam ; Calendar user type / delfromparam ; Delegator / deltoparam ; Delegatee / dirparam ; Directory entry / encodingparam ; Inline encoding / fmttypeparam ; Format type / fbtypeparam ; Free/busy time type / languageparam ; Language for text / memberparam ; Group or list membership / partstatparam ; Participation status / trigrelparam ; Alarm trigger relationship / reltypeparam ; Relationship type / roleparam ; Participation role / rsvpparam ; RSVP expectation / sentbyparam ; Sent by / tzidparam ; Reference to time zone object / valuetypeparam ; Property value data type / other-param other-param = (iana-param / x-param) iana-param = iana-token "=" param-value *("," param-value) ; Some other IANA registered iCalendar parameter. x-param = x-name "=" param-value *("," param-value) ; A non-standard, experimental parameter. 3.2.1. Alternate Text Representation Parameter Name: ALTREP Purpose: To specify an alternate text representation for the property value. Format Definition: This property parameter is defined by the following notation: altrepparam = "ALTREP" "=" DQUOTE uri DQUOTE Description: This parameter specifies a URI that points to an alternate representation for a textual property value. A property specifying this parameter MUST also include a value that reflects the default representation of the text value. The individual URI parameter values MUST each be specified in a quoted-string. Desruisseaux Expires September 3, 2007 [Page 14] Internet-Draft iCalendar March 2007 Example: DESCRIPTION;ALTREP="CID:part3.msg.970415T083000@example.com": Project XYZ Review Meeting will include the following agenda items: (a) Market Overview\, (b) Finances\, (c) Project Man agement The "ALTREP" property parameter value might point to a "text/html" content portion. Content-Type:text/html Content-Id:

Project XYZ Review Meeting will include the following agenda items:

  1. Market Overview
  2. Finances
  3. Project Management

3.2.2. Common Name Parameter Name: CN Purpose: To specify the common name to be associated with the calendar user specified by the property. Format Definition: This property parameter is defined by the following notation: cnparam = "CN" "=" param-value Description: This parameter can be specified on properties with a CAL-ADDRESS value type. The parameter specifies the common name to be associated with the calendar user specified by the property. The parameter value is text. The parameter value can be used for display text to be associated with the calendar address specified by the property. Desruisseaux Expires September 3, 2007 [Page 15] Internet-Draft iCalendar March 2007 Example: ORGANIZER;CN="John Smith":mailto:jsmith@example.com 3.2.3. Calendar User Type Parameter Name: CUTYPE Purpose: To specify the type of calendar user specified by the property. Format Definition: This property parameter is defined by the following notation: cutypeparam = "CUTYPE" "=" ("INDIVIDUAL" ; An individual / "GROUP" ; A group of individuals / "RESOURCE" ; A physical resource / "ROOM" ; A room resource / "UNKNOWN" ; Otherwise not known / x-name ; Experimental type / iana-token) ; Other IANA registered ; type ; Default is INDIVIDUAL Description: This parameter can be specified on properties with a CAL-ADDRESS value type. The parameter identifies the type of calendar user specified by the property. If not specified on a property that allows this parameter, the default is INDIVIDUAL. Example: ATTENDEE;CUTYPE=GROUP:mailto:ietf-calsch@example.org 3.2.4. Delegators Parameter Name: DELEGATED-FROM Purpose: To specify the calendar users that have delegated their participation to the calendar user specified by the property. Format Definition: This property parameter is defined by the following notation: delfromparam = "DELEGATED-FROM" "=" DQUOTE cal-address DQUOTE *("," DQUOTE cal-address DQUOTE) Desruisseaux Expires September 3, 2007 [Page 16] Internet-Draft iCalendar March 2007 Description: This parameter can be specified on properties with a CAL-ADDRESS value type. This parameter specifies those calendar users that have delegated their participation in a group scheduled event or to-do to the calendar user specified by the property. The value MUST be a mailto URI as defined in [RFC2368]. The individual calendar address parameter values MUST each be specified in a quoted-string. Example: ATTENDEE;DELEGATED-FROM="mailto:jsmith@example.com":mailto: jdoe@example.com 3.2.5. Delegatees Parameter Name: DELEGATED-TO Purpose: To specify the calendar users to whom the calendar user specified by the property has delegated participation. Format Definition: This property parameter is defined by the following notation: deltoparam = "DELEGATED-TO" "=" DQUOTE cal-address DQUOTE *("," DQUOTE cal-address DQUOTE) Description: This parameter can be specified on properties with a CAL-ADDRESS value type. This parameter specifies those calendar users whom have been delegated participation in a group scheduled event or to-do by the calendar user specified by the property. The value MUST be a mailto URI as defined in [RFC2368]. The individual calendar address parameter values MUST each be specified in a quoted-string. Example: ATTENDEE;DELEGATED-TO="mailto:jdoe@example.com","mailto:jqpublic @example.com":mailto:jsmith@example.com 3.2.6. Directory Entry Reference Parameter Name: DIR Purpose: To specify reference to a directory entry associated with the calendar user specified by the property. Desruisseaux Expires September 3, 2007 [Page 17] Internet-Draft iCalendar March 2007 Format Definition: This property parameter is defined by the following notation: dirparam = "DIR" "=" DQUOTE uri DQUOTE Description: This parameter can be specified on properties with a CAL-ADDRESS value type. The parameter specifies a reference to the directory entry associated with the calendar user specified by the property. The parameter value is a URI. The URI parameter value MUST be specified in a quoted-string. Example: ORGANIZER;DIR="ldap://example.com:6666/o=ABC%20Industries, c=US???(cn=Jim%20Dolittle)":mailto:jimdo@example.com 3.2.7. Inline Encoding Parameter Name: ENCODING Purpose: To specify an alternate inline encoding for the property value. Format Definition: This property parameter is defined by the following notation: encodingparam = "ENCODING" "=" ( "8BIT" ; "8bit" text encoding is defined in [RFC2045] / "BASE64" ; "BASE64" binary encoding format is defined in [RFC4648] ) Description: This property parameter identifies the inline encoding used in a property value. The default encoding is "8BIT", corresponding to a property value consisting of text. The "BASE64" encoding type corresponds to a property value encoded using the "BASE64" encoding defined in [RFC2045]. If the value type parameter is ";VALUE=BINARY", then the inline encoding parameter MUST be specified with the value ";ENCODING=BASE64". Example: ATTACH;FMTYPE=IMAGE/JPEG;ENCODING=BASE64;VALUE=BINARY:MIICajC CAdOgAwIBAgICBEUwDQYJKoZIhvcNAQEEBQAwdzELMAkGA1UEBhMCVVMxLDA qBgNVBAoTI05ldHNjYXBlIENvbW11bmljYXRpb25zIENvcnBvcmF0aW9uMRw Desruisseaux Expires September 3, 2007 [Page 18] Internet-Draft iCalendar March 2007 <...remainder of "BASE64" encoded binary data...> 3.2.8. Format Type Parameter Name: FMTTYPE Purpose: To specify the content type of a referenced object. Format Definition: This property parameter is defined by the following notation: fmttypeparam = "FMTTYPE" "=" type "/" subtype *(";" parameter) ; Where "type", "subtype", and "parameter" ; are defined in section 5.1 of [RFC2045] Description: This parameter can be specified on properties that are used to reference an object. The parameter specifies the content type of the referenced object. For example, on the "ATTACH" property, a FTP type URI value does not, by itself, necessarily convey the type of content associated with the resource. The parameter value MUST be the text for either an IANA registered media type or a non-standard media type. Example: ATTACH;FMTTYPE=application/msword:ftp://example.com/pub/docs/ agenda.doc 3.2.9. Free/Busy Time Type Parameter Name: FBTYPE Purpose: To specify the free or busy time type. Format Definition: This property parameter is defined by the following notation: fbtypeparam = "FBTYPE" "=" ("FREE" / "BUSY" / "BUSY-UNAVAILABLE" / "BUSY-TENTATIVE" / x-name ; Some experimental iCalendar free busy type. / iana-token) ; Some other IANA registered iCalendar free busy type. Desruisseaux Expires September 3, 2007 [Page 19] Internet-Draft iCalendar March 2007 Description: This parameter specifies the free or busy time type. The value FREE indicates that the time interval is free for scheduling. The value BUSY indicates that the time interval is busy because one or more events have been scheduled for that interval. The value BUSY-UNAVAILABLE indicates that the time interval is busy and that the interval can not be scheduled. The value BUSY-TENTATIVE indicates that the time interval is busy because one or more events have been tentatively scheduled for that interval. If not specified on a property that allows this parameter, the default is BUSY. Example: The following is an example of this parameter on a "FREEBUSY" property. FREEBUSY;FBTYPE=BUSY:19980415T133000Z/19980415T170000Z 3.2.10. Language Parameter Name: LANGUAGE Purpose: To specify the language for text values in a property or property parameter. Format Definition: This property parameter is defined by the following notation: languageparam = "LANGUAGE" "=" language language = Language-Tag ; As defined in [RFC4646] Description: This parameter identifies the language of the text in the property value and of all property parameter values of the property. The value of the "LANGUAGE" property parameter is that defined in [RFC4646]. For transport in a MIME entity, the Content-Language header field can be used to set the default language for the entire body part. Otherwise, no default language is assumed. Example: The following are examples of this parameter on the "SUMMARY" and "LOCATION" properties: SUMMARY;LANGUAGE=us-EN:Company Holiday Party LOCATION;LANGUAGE=en:Germany LOCATION;LANGUAGE=no:Tyskland Desruisseaux Expires September 3, 2007 [Page 20] Internet-Draft iCalendar March 2007 3.2.11. Group or List Membership Parameter Name: MEMBER Purpose: To specify the group or list membership of the calendar user specified by the property. Format Definition: This property parameter is defined by the following notation: memberparam = "MEMBER" "=" DQUOTE cal-address DQUOTE *("," DQUOTE cal-address DQUOTE) Description: This parameter can be specified on properties with a CAL-ADDRESS value type. The parameter identifies the groups or list membership for the calendar user specified by the property. The parameter value is either a single calendar address in a quoted-string or a COMMA character (US-ASCII decimal 44) separated list of calendar addresses, each in a quoted-string. The individual calendar address parameter values MUST each be specified in a quoted-string. Example: ATTENDEE;MEMBER="mailto:ietf-calsch@example.org":mailto: jsmith@example.com ATTENDEE;MEMBER="mailto:projectA@example.com","mailto:pr ojectB@example.com":mailto:janedoe@example.com 3.2.12. Participation Status Parameter Name: PARTSTAT Purpose: To specify the participation status for the calendar user specified by the property. Format Definition: This property parameter is defined by the following notation: Desruisseaux Expires September 3, 2007 [Page 21] Internet-Draft iCalendar March 2007 partstatparam = "PARTSTAT" "=" (partstat-event / partstat-todo / partstat-jour) partstat-event = ("NEEDS-ACTION" ; Event needs action / "ACCEPTED" ; Event accepted / "DECLINED" ; Event declined / "TENTATIVE" ; Event tentatively ; accepted / "DELEGATED" ; Event delegated / x-name ; Experimental status / iana-token) ; Other IANA registered ; status ; These are the participation statuses for a "VEVENT". ; Default is NEEDS-ACTION. partstat-todo = ("NEEDS-ACTION" ; To-do needs action / "ACCEPTED" ; To-do accepted / "DECLINED" ; To-do declined / "TENTATIVE" ; To-do tentatively ; accepted / "DELEGATED" ; To-do delegated / "COMPLETED" ; To-do completed. ; COMPLETED property has ; date/time completed. / "IN-PROCESS" ; To-do in process of ; being completed / x-name ; Experimental status / iana-token) ; Other IANA registered ; status ; These are the participation statuses for a "VTODO". ; Default is NEEDS-ACTION. partstat-jour = ("NEEDS-ACTION" ; Journal needs action / "ACCEPTED" ; Journal accepted / "DECLINED" ; Journal declined / x-name ; Experimental status / iana-token) ; Other IANA registered ; status ; These are the participation statuses for a "VJOURNAL". ; Default is NEEDS-ACTION. Description: This parameter can be specified on properties with a CAL-ADDRESS value type. The parameter identifies the participation status for the calendar user specified by the property value. The parameter values differ depending on whether they are associated with a group scheduled "VEVENT", "VTODO" or Desruisseaux Expires September 3, 2007 [Page 22] Internet-Draft iCalendar March 2007 "VJOURNAL". The values MUST match one of the values allowed for the given calendar component. If not specified on a property that allows this parameter, the default value is NEEDS-ACTION. Example: ATTENDEE;PARTSTAT=DECLINED:mailto:jsmith@example.com 3.2.13. Alarm Trigger Relationship Parameter Name: RELATED Purpose: To specify the relationship of the alarm trigger with respect to the start or end of the calendar component. Format Definition: This property parameter is defined by the following notation: trigrelparam = "RELATED" "=" ("START" ; Trigger off of start / "END") ; Trigger off of end Description: This parameter can be specified on properties that specify an alarm trigger with a "DURATION" value type. The parameter specifies whether the alarm will trigger relative to the start or end of the calendar component. The parameter value START will set the alarm to trigger off the start of the calendar component; the parameter value END will set the alarm to trigger off the end of the calendar component. If the parameter is not specified on an allowable property, then the default is START. Example: TRIGGER;RELATED=END:PT5M 3.2.14. Relationship Type Parameter Name: RELTYPE Purpose: To specify the type of hierarchical relationship associated with the calendar component specified by the property. Format Definition: This property parameter is defined by the following notation: Desruisseaux Expires September 3, 2007 [Page 23] Internet-Draft iCalendar March 2007 reltypeparam = "RELTYPE" "=" ("PARENT" ; Parent relationship. Default. / "CHILD" ; Child relationship / "SIBLING" ; Sibling relationship / iana-token ; Some other IANA registered ; iCalendar relationship type / x-name) ; A non-standard, experimental ; relationship type Description: This parameter can be specified on a property that references another related calendar. The parameter specifies the hierarchical relationship type of the calendar component referenced by the property. The parameter value can be PARENT, to indicate that the referenced calendar component is a superior of calendar component; CHILD to indicate that the referenced calendar component is a subordinate of the calendar component; SIBLING to indicate that the referenced calendar component is a peer of the calendar component. If this parameter is not specified on an allowable property, the default relationship type is PARENT. Example: RELATED-TO;RELTYPE=SIBLING:19960401-080045-4000F192713@ example.com 3.2.15. Participation Role Parameter Name: ROLE Purpose: To specify the participation role for the calendar user specified by the property. Format Definition: This property parameter is defined by the following notation: roleparam = "ROLE" "=" ("CHAIR" ; Indicates chair of the ; calendar entity / "REQ-PARTICIPANT" ; Indicates a participant whose ; participation is required / "OPT-PARTICIPANT" ; Indicates a participant whose ; participation is optional / "NON-PARTICIPANT" ; Indicates a participant who ; is copied for information ; purposes only / x-name ; Experimental role / iana-token) ; Other IANA role ; Default is REQ-PARTICIPANT Desruisseaux Expires September 3, 2007 [Page 24] Internet-Draft iCalendar March 2007 Description: This parameter can be specified on properties with a CAL-ADDRESS value type. The parameter specifies the participation role for the calendar user specified by the property in the group schedule calendar component. If not specified on a property that allows this parameter, the default value is REQ-PARTICIPANT. Example: ATTENDEE;ROLE=CHAIR:mailto:mrbig@example.com 3.2.16. RSVP Expectation Parameter Name: RSVP Purpose: To specify whether there is an expectation of a favor of a reply from the calendar user specified by the property value. Format Definition: This property parameter is defined by the following notation: rsvpparam = "RSVP" "=" ("TRUE" / "FALSE") ; Default is FALSE Description: This parameter can be specified on properties with a CAL-ADDRESS value type. The parameter identifies the expectation of a reply from the calendar user specified by the property value. This parameter is used by the "Organizer" to request a participation status reply from an "Attendee" of a group scheduled event or to-do. If not specified on a property that allows this parameter, the default value is FALSE. Example: ATTENDEE;RSVP=TRUE:mailto:jsmith@example.com 3.2.17. Sent By Parameter Name: SENT-BY Purpose: To specify the calendar user that is acting on behalf of the calendar user specified by the property. Format Definition: This property parameter is defined by the following notation: sentbyparam = "SENT-BY" "=" DQUOTE cal-address DQUOTE Desruisseaux Expires September 3, 2007 [Page 25] Internet-Draft iCalendar March 2007 Description: This parameter can be specified on properties with a CAL-ADDRESS value type. The parameter specifies the calendar user that is acting on behalf of the calendar user specified by the property. The parameter value MUST be a mailto URI as defined in [RFC2368]. The individual calendar address parameter values MUST each be specified in a quoted-string. Example: ORGANIZER;SENT-BY="mailto:sray@example.com":mailto: jsmith@example.com 3.2.18. Time Zone Identifier Parameter Name: TZID Purpose: To specify the identifier for the time zone definition for a time component in the property value. Format Definition: This property parameter is defined by the following notation: tzidparam = "TZID" "=" [tzidprefix] paramtext tzidprefix = "/" Description: This parameter MUST be specified on the "DTSTART", "DTEND", "DUE", "EXDATE" and "RDATE" properties when either a DATE-TIME or TIME value type is specified and when the value is not either a UTC or a "floating" time. Refer to the DATE-TIME or TIME value type definition for a description of UTC and "floating time" formats. This property parameter specifies a text value which uniquely identifies the "VTIMEZONE" calendar component to be used when evaluating the time portion of the property. The value of the "TZID" property parameter will be equal to the value of the "TZID" property for the matching time zone definition. An individual "VTIMEZONE" calendar component MUST be specified for each unique "TZID" parameter value specified in the iCalendar object. The parameter MUST be specified on properties with a DATE-TIME value if the DATE-TIME is not either a UTC or a "floating" time. The presence of the SOLIDUS character (US-ASCII decimal 47) as a prefix, indicates that this "TZID" represents a unique ID in a globally defined time zone registry (when such registry is defined). Desruisseaux Expires September 3, 2007 [Page 26] Internet-Draft iCalendar March 2007 Note: This document does not define a naming convention for time zone identifiers. Implementers may want to use the naming conventions defined in existing time zone specifications such as the public-domain TZ database [TZDB]. The specification of globally unique time zone identifiers is not addressed by this document and is left for future study. The following are examples of this property parameter: DTSTART;TZID=America/New_York:19980119T020000 DTEND;TZID=America/New_York:19980119T030000 The "TZID" property parameter MUST NOT be applied to DATE-TIME or TIME properties whose time values are specified in UTC. The use of local time in a DATE-TIME or TIME value without the "TZID" property parameter is to be interpreted as a local time value, regardless of the existence of "VTIMEZONE" calendar components in the iCalendar object. For more information see the sections on the value types DATE-TIME and TIME. 3.2.19. Value Data Types Parameter Name: VALUE Purpose: To explicitly specify the value type format for a property value. Format Definition: This property parameter is defined by the following notation: Desruisseaux Expires September 3, 2007 [Page 27] Internet-Draft iCalendar March 2007 valuetypeparam = "VALUE" "=" valuetype valuetype = ("BINARY" / "BOOLEAN" / "CAL-ADDRESS" / "DATE" / "DATE-TIME" / "DURATION" / "FLOAT" / "INTEGER" / "PERIOD" / "RECUR" / "TEXT" / "TIME" / "URI" / "UTC-OFFSET" / x-name ; Some experimental iCalendar value type. / iana-token) ; Some other IANA registered iCalendar value type. Description: This parameter specifies the value type and format of the property value. The property values MUST be of a single value type. For example, a "RDATE" property cannot have a combination of DATE-TIME and TIME value types. If the property's value is the default value type, then this parameter need not be specified. However, if the property's default value type is overridden by some other allowable value type, then this parameter MUST be specified. 3.3. Property Value Data Types The properties in an iCalendar object are strongly typed. The definition of each property restricts the value to be one of the value data types, or simply value types, defined in this section. The value type for a property will either be specified implicitly as the default value type or will be explicitly specified with the "VALUE" parameter. If the value type of a property is one of the alternate valid types, then it MUST be explicitly specified with the "VALUE" parameter. 3.3.1. Binary Desruisseaux Expires September 3, 2007 [Page 28] Internet-Draft iCalendar March 2007 Value Name: BINARY Purpose: This value type is used to identify properties that contain a character encoding of inline binary data. For example, an inline attachment of a document might be included in an iCalendar object. Format Definition: This value type is defined by the following notation: binary = *(4b-char) [b-end] ; A "BASE64" encoded character string, as defined by [RFC4648]. b-end = (2b-char "==") / (3b-char "=") b-char = ALPHA / DIGIT / "+" / "/" Description: Property values with this value type MUST also include the inline encoding parameter sequence of ";ENCODING=BASE64". That is, all inline binary data MUST first be character encoded using the "BASE64" encoding method defined in [RFC2045]. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. Example: The following is an abridged example of a "BASE64" encoded binary value data. JKoZIhvcNAQEEBQAwdzELMAkGA1UEBhMCVVMxLDAqBgNVBAoTI05ldHNjYXBlI ENvbW11bmljYXRpb25zIENvcnBvcmF0aW9uMRwwGgYDVQQLExNJbmZv <...remainder of "BASE64" encoded binary data...> 3.3.2. Boolean Value Name: BOOLEAN Purpose: This value type is used to identify properties that contain either a "TRUE" or "FALSE" Boolean value. Format Definition: This value type is defined by the following notation: boolean = "TRUE" / "FALSE" Description: These values are case insensitive text. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. Desruisseaux Expires September 3, 2007 [Page 29] Internet-Draft iCalendar March 2007 Example: The following is an example of a hypothetical property that has a BOOLEAN value type: TRUE 3.3.3. Calendar User Address Value Name: CAL-ADDRESS Purpose: This value type is used to identify properties that contain a calendar user address. Format Definition: This value type is defined by the following notation: cal-address = uri Description: The value is a URI as defined by [RFC3986] or any other IANA registered form for a URI. When used to address an Internet email transport address for a calendar user, the value MUST be a mailto URI, as defined by [RFC2368]. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. Example: mailto:jane_doe@example.com 3.3.4. Date Value Name: DATE Purpose: This value type is used to identify values that contain a calendar date. Format Definition: This value type is defined by the following notation: date = date-value date-value = date-fullyear date-month date-mday date-fullyear = 4DIGIT date-month = 2DIGIT ;01-12 date-mday = 2DIGIT ;01-28, 01-29, 01-30, 01-31 ;based on month/year Desruisseaux Expires September 3, 2007 [Page 30] Internet-Draft iCalendar March 2007 Description: If the property permits, multiple "date" values are specified as a COMMA character (US-ASCII decimal 44) separated list of values. The format for the value type is expressed as the [ISO.8601.1988] complete representation, basic format for a calendar date. The textual format specifies a four-digit year, two-digit month, and two-digit day of the month. There are no separator characters between the year, month and day component text. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. Example: The following represents July 14, 1997: 19970714 3.3.5. Date-Time Value Name: DATE-TIME Purpose: This value type is used to identify values that specify a precise calendar date and time of day. Format Definition: This value type is defined by the following notation: date-time = date "T" time ;As specified in the date and time ;value definitions Description: If the property permits, multiple "date-time" values are specified as a COMMA character (US-ASCII decimal 44) separated list of values. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. The "DATE-TIME" value type is used to identify values that contain a precise calendar date and time of day. The format is based on the [ISO.8601.1988] complete representation, basic format for a calendar date and time of day. The text format is a concatenation of the "date", followed by the LATIN CAPITAL LETTER T character (US-ASCII decimal 84) time designator, followed by the "time" format. The "DATE-TIME" value type expresses time values in three forms: The form of date and time with UTC offset MUST NOT be used. For example, the following is not valid for a date-time value: 19980119T230000-0800 ;Invalid time format Desruisseaux Expires September 3, 2007 [Page 31] Internet-Draft iCalendar March 2007 FORM #1: DATE WITH LOCAL TIME The date with local time form is simply a date-time value that does not contain the UTC designator nor does it reference a time zone. For example, the following represents January 18, 1998, at 11 PM: 19980118T230000 Date-time values of this type are said to be "floating" and are not bound to any time zone in particular. They are used to represent the same hour, minute, and second value regardless of which time zone is currently being observed. For example, an event can be defined that indicates that an individual will be busy from 11:00 AM to 1:00 PM every day, no matter which time zone the person is in. In these cases, a local time can be specified. The recipient of an iCalendar object with a property value consisting of a local time, without any relative time zone information, SHOULD interpret the value as being fixed to whatever time zone the "ATTENDEE" is in at any given moment. This means that two "Attendees", in different time zones, receiving the same event definition as a floating time, may be participating in the event at different actual times. Floating time SHOULD only be used where that is the reasonable behavior. In most cases, a fixed time is desired. To properly communicate a fixed time in a property value, either UTC time or local time with time zone reference MUST be specified. The use of local time in a DATE-TIME value without the "TZID" property parameter is to be interpreted as floating time, regardless of the existence of "VTIMEZONE" calendar components in the iCalendar object. FORM #2: DATE WITH UTC TIME The date with UTC time, or absolute time, is identified by a LATIN CAPITAL LETTER Z suffix character (US-ASCII decimal 90), the UTC designator, appended to the time value. For example, the following represents January 19, 1998, at 0700 UTC: 19980119T070000Z The "TZID" property parameter MUST NOT be applied to DATE-TIME properties whose time values are specified in UTC. Desruisseaux Expires September 3, 2007 [Page 32] Internet-Draft iCalendar March 2007 FORM #3: DATE WITH LOCAL TIME AND TIME ZONE REFERENCE The date and local time with reference to time zone information is identified by the use the "TZID" property parameter to reference the appropriate time zone definition. "TZID" is discussed in detail in Section 3.2.18. For example, the following represents 2:00 A.M. in New York on Janurary 19, 1998: TZID=America/New_York:19980119T020000 Example: The following represents July 14, 1997, at 1:30 PM in New York City in each of the three time formats, using the "DTSTART" property. DTSTART:19970714T133000 ; Local time DTSTART:19970714T173000Z ; UTC time DTSTART;TZID=America/New_York:19970714T133000 ; Local time and time ; zone reference A time value MUST only specify the second 60 when specifying a positive "leap second" . For example: 19970630T235960Z 3.3.6. Duration Value Name: DURATION Purpose: This value type is used to identify properties that contain a duration of time. Format Definition: This value type is defined by the following notation: dur-value = (["+"] / "-") "P" (dur-date / dur-time / dur-week) dur-date = dur-day [dur-time] dur-time = "T" (dur-hour / dur-minute / dur-second) dur-week = 1*DIGIT "W" dur-hour = 1*DIGIT "H" [dur-minute] dur-minute = 1*DIGIT "M" [dur-second] dur-second = 1*DIGIT "S" dur-day = 1*DIGIT "D" Desruisseaux Expires September 3, 2007 [Page 33] Internet-Draft iCalendar March 2007 Description: If the property permits, multiple "duration" values are specified by a COMMA character (US-ASCII decimal 44) separated list of values. The format is expressed as the [ISO.8601.1988] basic format for the duration of time. The format can represent durations in terms of weeks, days, hours, minutes, and seconds. Negative durations are typically used to schedule an alarm to trigger before an associated time (see Section 3.8.6.3). No additional content value encoding (i.e., BACKSLASH character encoding) are defined for this value type. Example: A duration of 15 days, 5 hours and 20 seconds would be: P15DT5H0M20S A duration of 7 weeks would be: P7W 3.3.7. Float Value Name: FLOAT Purpose: This value type is used to identify properties that contain a real number value. Format Definition: This value type is defined by the following notation: float = (["+"] / "-") 1*DIGIT ["." 1*DIGIT] Description: If the property permits, multiple "float" values are specified by a COMMA character (US-ASCII decimal 44) separated list of values. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. Example: 1000000.0000001 1.333 -3.14 Desruisseaux Expires September 3, 2007 [Page 34] Internet-Draft iCalendar March 2007 3.3.8. Integer Value Name: INTEGER Purpose: This value type is used to identify properties that contain a signed integer value. Format Definition: This value type is defined by the following notation: integer = (["+"] / "-") 1*DIGIT Description: If the property permits, multiple "integer" values are specified by a COMMA character (US-ASCII decimal 44) separated list of values. The valid range for "integer" is -2147483648 to 2147483647. If the sign is not specified, then the value is assumed to be positive. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. Example: 1234567890 -1234567890 +1234567890 432109876 3.3.9. Period of Time Value Name: PERIOD Purpose: This value type is used to identify values that contain a precise period of time. Format Definition: This value type is defined by the following notation: period = period-explicit / period-start period-explicit = date-time "/" date-time ; [ISO.8601.1988] complete representation basic format for a ; period of time consisting of a start and end. The start MUST ; be before the end. period-start = date-time "/" dur-value ; [ISO.8601.1988] complete representation basic format for a ; period of time consisting of a start and positive duration Desruisseaux Expires September 3, 2007 [Page 35] Internet-Draft iCalendar March 2007 ; of time. Description: If the property permits, multiple "period" values are specified by a COMMA character (US-ASCII decimal 44) separated list of values. There are two forms of a period of time. First, a period of time is identified by its start and its end. This format is expressed as the [ISO.8601.1988] complete representation, basic format for "DATE-TIME" start of the period, followed by a SOLIDUS character (US-ASCII decimal 47), followed by the "DATE-TIME" of the end of the period. The start of the period MUST be before the end of the period. Second, a period of time can also be defined by a start and a positive duration of time. The format is expressed as the [ISO.8601.1988] complete representation, basic format for the "DATE-TIME" start of the period, followed by a SOLIDUS character (US-ASCII decimal 47), followed by the [ISO.8601.1988] basic format for "DURATION" of the period. Example: The period starting at 18:00:00 UTC, on January 1, 1997 and ending at 07:00:00 UTC on January 2, 1997 would be: 19970101T180000Z/19970102T070000Z The period start at 18:00:00 on January 1, 1997 and lasting 5 hours and 30 minutes would be: 19970101T180000Z/PT5H30M No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. 3.3.10. Recurrence Rule Value Name: RECUR Purpose: This value type is used to identify properties that contain a recurrence rule specification. Format Definition: This value type is defined by the following notation: recur = recur-rule-part *( ";" recur-rule-part ) ; ; The rule parts are not ordered in any ; particular sequence ; ; The FREQ rule part is REQUIRED, ; but MUST NOT occur more than once Desruisseaux Expires September 3, 2007 [Page 36] Internet-Draft iCalendar March 2007 ; ; The UNTIL or COUNT rule parts are OPTIONAL, ; but they MUST NOT occur in the same 'recur' ; ; The other rule parts are OPTIONAL, ; but MUST NOT occur more than once recur-rule-part = ( "FREQ" "=" freq ) / ( "UNTIL" "=" enddate ) / ( "COUNT" "=" 1*DIGIT ) / ( "INTERVAL" "=" 1*DIGIT ) / ( "BYSECOND" "=" byseclist ) / ( "BYMINUTE" "=" byminlist ) / ( "BYHOUR" "=" byhrlist ) / ( "BYDAY" "=" bywdaylist ) / ( "BYMONTHDAY" "=" bymodaylist ) / ( "BYYEARDAY" "=" byyrdaylist ) / ( "BYWEEKNO" "=" bywknolist ) / ( "BYMONTH" "=" bymolist ) / ( "BYSETPOS" "=" bysplist ) / ( "WKST" "=" weekday ) freq = "SECONDLY" / "MINUTELY" / "HOURLY" / "DAILY" / "WEEKLY" / "MONTHLY" / "YEARLY" enddate = date / date-time ;A UTC value byseclist = ( seconds *("," seconds) ) seconds = 1*2DIGIT ;0 to 60 byminlist = ( minutes *("," minutes) ) minutes = 1*2DIGIT ;0 to 59 byhrlist = ( hour *("," hour) ) hour = 1*2DIGIT ;0 to 23 bywdaylist = ( weekdaynum *("," weekdaynum) ) weekdaynum = [[plus / minus] ordwk] weekday plus = "+" minus = "-" ordwk = 1*2DIGIT ;1 to 53 Desruisseaux Expires September 3, 2007 [Page 37] Internet-Draft iCalendar March 2007 weekday = "SU" / "MO" / "TU" / "WE" / "TH" / "FR" / "SA" ;Corresponding to SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, ;FRIDAY, and SATURDAY days of the week. bymodaylist = ( monthdaynum *("," monthdaynum) ) monthdaynum = [plus / minus] ordmoday ordmoday = 1*2DIGIT ;1 to 31 byyrdaylist = ( yeardaynum *("," yeardaynum) ) yeardaynum = [plus / minus] ordyrday ordyrday = 1*3DIGIT ;1 to 366 bywknolist = ( weeknum *("," weeknum) ) weeknum = [plus / minus] ordwk bymolist = ( monthnum *("," monthnum) ) monthnum = 1*2DIGIT ;1 to 12 bysplist = ( setposday *("," setposday) ) setposday = yeardaynum Description: This value type is a structured value consisting of a list of one or more recurrence grammar parts. Each rule part is defined by a NAME=VALUE pair. The rule parts are separated from each other by the SEMICOLON character (US-ASCII decimal 59). The rule parts are not ordered in any particular sequence. Individual rule parts MUST only be specified once. Note: Compliant applications MUST accept rule parts ordered in any sequence, but to ensure backward compatibility with applications that pre-date this revision of iCalendar the FREQ rule part MUST be the first rule part specified in a RECUR value. The FREQ rule part identifies the type of recurrence rule. This rule part MUST be specified in the recurrence rule. Valid values include SECONDLY, to specify repeating events based on an interval of a second or more; MINUTELY, to specify repeating events based on an interval of a minute or more; HOURLY, to specify repeating events based on an interval of an hour or more; DAILY, to specify repeating events based on an interval of a day or more; WEEKLY, to Desruisseaux Expires September 3, 2007 [Page 38] Internet-Draft iCalendar March 2007 specify repeating events based on an interval of a week or more; MONTHLY, to specify repeating events based on an interval of a month or more; and YEARLY, to specify repeating events based on an interval of a year or more. The INTERVAL rule part contains a positive integer representing how often the recurrence rule repeats. The default value is "1", meaning every second for a SECONDLY rule, or every minute for a MINUTELY rule, every hour for an HOURLY rule, every day for a DAILY rule, every week for a WEEKLY rule, every month for a MONTHLY rule and every year for a YEARLY rule. The UNTIL rule part defines a DATE or DATE-TIME value which bounds the recurrence rule in an inclusive manner. If the value specified by UNTIL is synchronized with the specified recurrence, this DATE or DATE-TIME becomes the last instance of the recurrence. The value of the UNTIL rule part MUST have the same value type as the "DTSTART" property. If specified as a DATE-TIME value, then it MUST be specified in a UTC time format. If not present, and the COUNT rule part is also not present, the "RRULE" is considered to repeat forever. The COUNT rule part defines the number of occurrences at which to range-bound the recurrence. The "DTSTART" property value always counts as the first occurrence. The BYSECOND rule part specifies a COMMA character (US-ASCII decimal 44) separated list of seconds within a minute. Valid values are 0 to 60. The BYMINUTE rule part specifies a COMMA character (US-ASCII decimal 44) separated list of minutes within an hour. Valid values are 0 to 59. The BYHOUR rule part specifies a COMMA character (US-ASCII decimal 44) separated list of hours of the day. Valid values are 0 to 23. The BYSECOND, BYMINUTE and BYHOUR rule parts MUST NOT be specified when the associated "DTSTART" property has a DATE value type. These rule parts MUST be ignored in RECUR value that violate the above requirement (e.g., generated by applications that pre-date this revision of iCalendar). The BYDAY rule part specifies a COMMA character (US-ASCII decimal 44) separated list of days of the week; SU indicates Sunday; MO indicates Monday; TU indicates Tuesday; WE indicates Wednesday; TH indicates Thursday; FR indicates Friday; SA indicates Saturday. Each BYDAY value can also be preceded by a positive (+n) or negative (-n) integer. If present, this indicates the nth occurrence of the specific day within the MONTHLY or YEARLY "RRULE". For example, within a MONTHLY rule, +1MO (or simply 1MO) Desruisseaux Expires September 3, 2007 [Page 39] Internet-Draft iCalendar March 2007 represents the first Monday within the month, whereas -1MO represents the last Monday of the month. If an integer modifier is not present, it means all days of this type within the specified frequency. For example, within a MONTHLY rule, MO represents all Mondays within the month. The BYMONTHDAY rule part specifies a COMMA character (US-ASCII decimal 44) separated list of days of the month. Valid values are 1 to 31 or -31 to -1. For example, -10 represents the tenth to the last day of the month. The BYYEARDAY rule part specifies a COMMA character (US-ASCII decimal 44) separated list of days of the year. Valid values are 1 to 366 or -366 to -1. For example, -1 represents the last day of the year (December 31st) and -306 represents the 306th to the last day of the year (March 1st). The BYWEEKNO rule part specifies a COMMA character (US-ASCII decimal 44) separated list of ordinals specifying weeks of the year. Valid values are 1 to 53 or -53 to -1. This corresponds to weeks according to week numbering as defined in [ISO.8601.1988]. A week is defined as a seven day period, starting on the day of the week defined to be the week start (see WKST). Week number one of the calendar year is the first week which contains at least four (4) days in that calendar year. This rule part is only valid for YEARLY rules. For example, 3 represents the third week of the year. Note: Assuming a Monday week start, week 53 can only occur when Thursday is January 1 or if it is a leap year and Wednesday is January 1. The BYMONTH rule part specifies a COMMA character (US-ASCII decimal 44) separated list of months of the year. Valid values are 1 to 12. The WKST rule part specifies the day on which the workweek starts. Valid values are MO, TU, WE, TH, FR, SA and SU. This is significant when a WEEKLY "RRULE" has an interval greater than 1, and a BYDAY rule part is specified. This is also significant when in a YEARLY "RRULE" when a BYWEEKNO rule part is specified. The default value is MO. The BYSETPOS rule part specifies a COMMA character (US-ASCII decimal 44) separated list of values which corresponds to the nth occurrence within the set of events specified by the rule. Valid values are 1 to 366 or -366 to -1. It MUST only be used in conjunction with another BYxxx rule part. For example "the last Desruisseaux Expires September 3, 2007 [Page 40] Internet-Draft iCalendar March 2007 work day of the month" could be represented as: FREQ=MONTHLY;BYDAY=MO,TU,WE,TH,FR;BYSETPOS=-1 Each BYSETPOS value can include a positive (+n) or negative (-n) integer. If present, this indicates the nth occurrence of the specific occurrence within the set of occurences specified by the rule. Recurrence rules may generate recurrence instances with invalid date (e.g., February 30) or nonexistent local time (e.g., 1:30 AM on a day where the local time is moved forward by an hour at 1:00 AM). Such recurrence instances MUST be ignored and MUST NOT be counted as part of the recurrence set. Information, not contained in the rule, necessary to determine the various recurrence instance start time and dates are derived from the Start Time ("DTSTART") component attribute. For example, "FREQ=YEARLY;BYMONTH=1" doesn't specify a specific day within the month or a time. This information would be the same as what is specified for "DTSTART". BYxxx rule parts modify the recurrence in some manner. BYxxx rule parts for a period of time which is the same or greater than the frequency generally reduce or limit the number of occurrences of the recurrence generated. For example, "FREQ=DAILY;BYMONTH=1" reduces the number of recurrence instances from all days (if BYMONTH rule part is not present) to all days in January. BYxxx rule parts for a period of time less than the frequency generally increase or expand the number of occurrences of the recurrence. For example, "FREQ=YEARLY;BYMONTH=1,2" increases the number of days within the yearly recurrence set from 1 (if BYMONTH rule part is not present) to 2. If multiple BYxxx rule parts are specified, then after evaluating the specified FREQ and INTERVAL rule parts, the BYxxx rule parts are applied to the current set of evaluated occurrences in the following order: BYMONTH, BYWEEKNO, BYYEARDAY, BYMONTHDAY, BYDAY, BYHOUR, BYMINUTE, BYSECOND and BYSETPOS; then COUNT and UNTIL are evaluated. Here is an example of evaluating multiple BYxxx rule parts. DTSTART;TZID=America/New_York:19970105T083000 RRULE:FREQ=YEARLY;INTERVAL=2;BYMONTH=1;BYDAY=SU;BYHOUR=8,9; BYMINUTE=30 First, the "INTERVAL=2" would be applied to "FREQ=YEARLY" to Desruisseaux Expires September 3, 2007 [Page 41] Internet-Draft iCalendar March 2007 arrive at "every other year". Then, "BYMONTH=1" would be applied to arrive at "every January, every other year". Then, "BYDAY=SU" would be applied to arrive at "every Sunday in January, every other year". Then, "BYHOUR=8,9" would be applied to arrive at "every Sunday in January at 8 AM and 9 AM, every other year". Then, "BYMINUTE=30" would be applied to arrive at "every Sunday in January at 8:30 AM and 9:30 AM, every other year". Then, lacking information from "RRULE", the second is derived from "DTSTART", to end up in "every Sunday in January at 8:30:00 AM and 9:30:00 AM, every other year". Similarly, if the BYMINUTE, BYHOUR, BYDAY, BYMONTHDAY or BYMONTH rule part were missing, the appropriate minute, hour, day or month would have been retrieved from the "DTSTART" property. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. Example: The following is a rule which specifies 10 occurences which occur every other day: FREQ=DAILY;COUNT=10;INTERVAL=2 There are other examples specified in Section 3.8.5.3. 3.3.11. Text Value Name: TEXT Purpose: This value type is used to identify values that contain human readable text. Format Definition: This value type is defined by the following notation. text = *(TSAFE-CHAR / ":" / DQUOTE / ESCAPED-CHAR) ; Folded according to description above ESCAPED-CHAR = ("\\" / "\;" / "\," / "\N" / "\n") ; \\ encodes \, \N or \n encodes newline ; \; encodes ;, \, encodes , TSAFE-CHAR = %x20-21 / %x23-2B / %x2D-39 / %x3C-5B / %x5D-7E / NON-US-ASCII ; Any character except CTLs not needed by the current ; character set, DQUOTE, ";", ":", "\", "," Desruisseaux Expires September 3, 2007 [Page 42] Internet-Draft iCalendar March 2007 Description: If the property permits, multiple TEXT values are specified by a COMMA character (US-ASCII decimal 44) separated list of values. The language in which the text is represented can be controlled by the "LANGUAGE" property parameter. An intentional formatted text line break MUST only be included in a "TEXT" property value by representing the line break with the character sequence of BACKSLASH (US-ASCII decimal 92), followed by a LATIN SMALL LETTER N (US-ASCII decimal 110) or a LATIN CAPITAL LETTER N (US-ASCII decimal 78), that is "\n" or "\N". The "TEXT" property values may also contain special characters that are used to signify delimiters, such as a COMMA character for lists of values or a SEMICOLON character for structured values. In order to support the inclusion of these special characters in "TEXT" property values, they MUST be escaped with a BACKSLASH character. A BACKSLASH character (US-ASCII decimal 92) in a "TEXT" property value MUST be escaped with another BACKSLASH character. A COMMA character in a "TEXT" property value MUST be escaped with a BACKSLASH character (US-ASCII decimal 92). A SEMICOLON character in a "TEXT" property value MUST be escaped with a BACKSLASH character (US-ASCII decimal 92). However, a COLON character in a "TEXT" property value SHALL NOT be escaped with a BACKSLASH character. Example: A multiple line value of: Project XYZ Final Review Conference Room - 3B Come Prepared. would be represented as: Project XYZ Final Review\nConference Room - 3B\nCome Prepared. 3.3.12. Time Value Name: TIME Purpose: This value type is used to identify values that contain a time of day. Format Definition: This value type is defined by the following notation: Desruisseaux Expires September 3, 2007 [Page 43] Internet-Draft iCalendar March 2007 time = time-hour time-minute time-second [time-utc] time-hour = 2DIGIT ;00-23 time-minute = 2DIGIT ;00-59 time-second = 2DIGIT ;00-60 ;The "60" value is used to account for positive "leap" seconds. time-utc = "Z" Description: If the property permits, multiple "time" values are specified by a COMMA character (US-ASCII decimal 44) separated list of values. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. The "TIME" value type is used to identify values that contain a time of day. The format is based on the [ISO.8601.1988] complete representation, basic format for a time of day. The text format consists of a two-digit 24-hour of the day (i.e., values 00-23), two-digit minute in the hour (i.e., values 00-59), and two-digit seconds in the minute (i.e., values 00-60). The seconds value of 60 MUST only be used to account for positive "leap" seconds. Fractions of a second are not supported by this format. In parallel to the "DATE-TIME" definition above, the "TIME" value type expresses time values in three forms: The form of time with UTC offset MUST NOT be used. For example, the following is not valid for a time value: 230000-0800 ;Invalid time format FORM #1 LOCAL TIME The local time form is simply a time value that does not contain the UTC designator nor does it reference a time zone. For example, 11:00 PM: 230000 Time values of this type are said to be "floating" and are not bound to any time zone in particular. They are used to represent the same hour, minute, and second value regardless of which time zone is currently being observed. For example, an event can be defined that indicates that an individual will be busy from 11:00 AM to 1:00 PM every day, no matter which time zone the person is in. In these cases, a local time can be specified. The recipient of an iCalendar object with a property value consisting of a local time, without any relative time zone information, SHOULD interpret Desruisseaux Expires September 3, 2007 [Page 44] Internet-Draft iCalendar March 2007 the value as being fixed to whatever time zone the "ATTENDEE" is in at any given moment. This means that two "Attendees", may participate in the same event at different UTC times; floating time SHOULD only be used where that is reasonable behavior. In most cases, a fixed time is desired. To properly communicate a fixed time in a property value, either UTC time or local time with time zone reference MUST be specified. The use of local time in a TIME value without the "TZID" property parameter is to be interpreted as a local time value, regardless of the existence of "VTIMEZONE" calendar components in the iCalendar object. FORM #2: UTC TIME UTC time, or absolute time, is identified by a LATIN CAPITAL LETTER Z suffix character (US-ASCII decimal 90), the UTC designator, appended to the time value. For example, the following represents 07:00 AM UTC: 070000Z The "TZID" property parameter MUST NOT be applied to TIME properties whose time values are specified in UTC. FORM #3: LOCAL TIME AND TIME ZONE REFERENCE The local time with reference to time zone information form is identified by the use the "TZID" property parameter to reference the appropriate time zone definition. "TZID" is discussed in detail in Section 3.2.18. Example: The following represents 8:30 AM in New York in Winter, five hours behind UTC, in each of the three formats : 083000 133000Z TZID=America/New_York:083000 3.3.13. URI Value Name: URI Desruisseaux Expires September 3, 2007 [Page 45] Internet-Draft iCalendar March 2007 Purpose: This value type is used to identify values that contain a uniform resource identifier (URI) type of reference to the property value. Format Definition: This value type is defined by the following notation: uri = Description: This value type might be used to reference binary information, for values that are large, or otherwise undesirable to include directly in the iCalendar object. Property values with this value type MUST follow the generic URI syntax defined in [RFC3986]. When a property parameter value is a URI value type, the URI MUST be specified as a quoted-string value. No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. Example: The following is a URI for a network file: http://example.com/my-report.txt 3.3.14. UTC Offset Value Name: UTC-OFFSET Purpose: This value type is used to identify properties that contain an offset from UTC to local time. Format Definition: This value type is defined by the following notation: utc-offset = time-numzone time-numzone = ("+" / "-") time-hour time-minute [time-second] Description: The PLUS SIGN (US-ASCII decimal 43) character MUST be specified for positive UTC offsets (i.e., ahead of UTC). The HYPHEN-MINUS character (US-ASCII decimal 45) MUST be specified for negative UTC offsets (i.e., behind of UTC). The value of "-0000" and "-000000" are not allowed. The time-second, if present, MUST NOT be 60; if absent, it defaults to zero. Desruisseaux Expires September 3, 2007 [Page 46] Internet-Draft iCalendar March 2007 No additional content value encoding (i.e., BACKSLASH character encoding) is defined for this value type. Example: The following UTC offsets are given for standard time for New York (five hours behind UTC) and Geneva (one hour ahead of UTC): -0500 +0100 3.4. iCalendar Object The Calendaring and Scheduling Core Object is a collection of calendaring and scheduling information. Typically, this information will consist of an iCalendar stream with a single iCalendar object. However, multiple iCalendar objects can be sequentially grouped together in an iCalendar stream. The first line and last line of the iCalendar object MUST contain a pair of iCalendar object delimiter strings. The syntax for an iCalendar stream is as follows: icalstream = 1*icalobject icalobject = "BEGIN" ":" "VCALENDAR" CRLF icalbody "END" ":" "VCALENDAR" CRLF The following is a simple example of an iCalendar object: BEGIN:VCALENDAR VERSION:2.0 PRODID:-//hacksw/handcal//NONSGML v1.0//EN BEGIN:VEVENT UID:19970610T172345Z-AF23B2@example.com DTSTAMP:19970610T172345Z DTSTART:19970714T170000Z DTEND:19970715T035959Z SUMMARY:Bastille Day Party END:VEVENT END:VCALENDAR 3.5. Property A property is the definition of an individual attribute describing a calendar object or a calendar component. A property takes the form defined by the "contentline" notation defined in Section 3.1. The following is an example of a property: Desruisseaux Expires September 3, 2007 [Page 47] Internet-Draft iCalendar March 2007 DTSTART:19960415T133000Z This memo imposes no ordering of properties within an iCalendar object. Property names, parameter names and enumerated parameter values are case insensitive. For example, the property name "DUE" is the same as "due" and "Due", DTSTART;TZID=America/New_York:19980714T120000 is the same as DtStart;TzID=America/New_York:19980714T120000. 3.6. Calendar Components The body of the iCalendar object consists of a sequence of calendar properties and one or more calendar components. The calendar properties are attributes that apply to the calendar object as a whole. The calendar components are collections of properties that express a particular calendar semantic. For example, the calendar component can specify an event, a to-do, a journal entry, time zone information, free/busy time information, or an alarm. The body of the iCalendar object is defined by the following notation: Desruisseaux Expires September 3, 2007 [Page 48] Internet-Draft iCalendar March 2007 icalbody = calprops component calprops = *( ; the following are REQUIRED, ; but MUST NOT occur more than once prodid / version / ; the following are OPTIONAL, ; but MUST NOT occur more than once calscale / method / ; the following are OPTIONAL, ; and MAY occur more than once x-prop / iana-prop ) component = 1*(eventc / todoc / journalc / freebusyc / timezonec / iana-comp / x-comp) iana-comp = "BEGIN" ":" iana-token CRLF 1*contentline "END" ":" iana-token CRLF x-comp = "BEGIN" ":" x-name CRLF 1*contentline "END" ":" x-name CRLF An iCalendar object MUST include the "PRODID" and "VERSION" calendar properties. In addition, it MUST include at least one calendar component. Special forms of iCalendar objects are possible to publish just busy time (i.e., only a "VFREEBUSY" calendar component) or time zone (i.e., only a "VTIMEZONE" calendar component) information. In addition, a complex iCalendar object that is used to capture a complete snapshot of the contents of a calendar is possible (e.g., composite of many different calendar components). More commonly, an iCalendar object will consist of just a single "VEVENT", "VTODO" or "VJOURNAL" calendar component. 3.6.1. Event Component Desruisseaux Expires September 3, 2007 [Page 49] Internet-Draft iCalendar March 2007 Component Name: VEVENT Purpose: Provide a grouping of component properties that describe an event. Format Definition: A "VEVENT" calendar component is defined by the following notation: eventc = "BEGIN" ":" "VEVENT" CRLF eventprop *alarmc "END" ":" "VEVENT" CRLF eventprop = *( ; the following are REQUIRED, ; but MUST NOT occur more than once dtstamp / dtstart / uid / ; the following are OPTIONAL, ; but MUST NOT occur more than once class / created / description / geo / last-mod / location / organizer / priority / seq / status / summary / transp / url / recurid / ; the following is OPTIONAL, ; but SHOULD NOT occur more than once rrule / ; either 'dtend' or 'duration' MAY appear in ; a 'eventprop', but 'dtend' and 'duration' ; MUST NOT occur in the same 'eventprop' dtend / duration / ; the following are OPTIONAL, ; and MAY occur more than once attach / attendee / categories / comment / contact / exdate / rstatus / related / resources / rdate / x-prop / iana-prop ) Desruisseaux Expires September 3, 2007 [Page 50] Internet-Draft iCalendar March 2007 Description: A "VEVENT" calendar component is a grouping of component properties, and possibly including "VALARM" calendar components, that represents a scheduled amount of time on a calendar. For example, it can be an activity; such as a one-hour long, department meeting from 8:00 AM to 9:00 AM, tomorrow. Generally, an event will take up time on an individual calendar. Hence, the event will appear as an opaque interval in a search for busy time. Alternately, the event can have its Time Transparency set to "TRANSPARENT" in order to prevent blocking of the event in searches for busy time. The "VEVENT" is also the calendar component used to specify an anniversary or daily reminder within a calendar. These events have a DATE value type for the "DTSTART" property instead of the default value type of DATE-TIME. If such a "VEVENT" has a "DTEND" property, it MUST be specified as a DATE value also. The anniversary type of "VEVENT" can span more than one date (i.e., "DTEND" property value is set to a calendar date after the "DTSTART" property value). If such a "VEVENT" has a "DURATION" property, it MUST be specified as a "dur-day" or "dur-week" value. The "DTSTART" property for a "VEVENT" specifies the inclusive start of the event. For recurring events, it also specifies the very first instance in the recurrence set. The "DTEND" property for a "VEVENT" calendar component specifies the non-inclusive end of the event. For cases where a "VEVENT" calendar component specifies a "DTSTART" property with a DATE value type but no "DTEND" nor DURATION property, the event's duration is taken to be one day. For cases where a "VEVENT" calendar component specifies a "DTSTART" property with a DATE-TIME value type but no "DTEND" property, the event ends on the same calendar date and time of day specified by the "DTSTART" property. The "VEVENT" calendar component cannot be nested within another calendar component. However, "VEVENT" calendar components can be related to each other or to a "VTODO" or to a "VJOURNAL" calendar component with the "RELATED-TO" property. Example: The following is an example of the "VEVENT" calendar component used to represent a meeting that will also be opaque to searches for busy time: Desruisseaux Expires September 3, 2007 [Page 51] Internet-Draft iCalendar March 2007 BEGIN:VEVENT UID:19970901T130000Z-123401@example.com DTSTAMP:19970901T130000Z DTSTART:19970903T163000Z DTEND:19970903T190000Z SUMMARY:Annual Employee Review CLASS:PRIVATE CATEGORIES:BUSINESS,HUMAN RESOURCES END:VEVENT The following is an example of the "VEVENT" calendar component used to represent a reminder that will not be opaque, but rather transparent, to searches for busy time: BEGIN:VEVENT UID:19970901T130000Z-123402@example.com DTSTAMP:19970901T130000Z DTSTART:19970401T163000Z DTEND:19970402T010000Z SUMMARY:Laurel is in sensitivity awareness class. CLASS:PUBLIC CATEGORIES:BUSINESS,HUMAN RESOURCES TRANSP:TRANSPARENT END:VEVENT The following is an example of the "VEVENT" calendar component used to represent an anniversary that will occur annually. BEGIN:VEVENT UID:19970901T130000Z-123403@example.com DTSTAMP:19970901T130000Z DTSTART;VALUE=DATE:19971102 SUMMARY:Our Blissful Anniversary TRANSP:TRANSPARENT CLASS:CONFIDENTIAL CATEGORIES:ANNIVERSARY,PERSONAL,SPECIAL OCCASION RRULE:FREQ=YEARLY END:VEVENT 3.6.2. To-do Component Component Name: VTODO Purpose: Provide a grouping of calendar properties that describe a to-do. Desruisseaux Expires September 3, 2007 [Page 52] Internet-Draft iCalendar March 2007 Format Definition: A "VTODO" calendar component is defined by the following notation: todoc = "BEGIN" ":" "VTODO" CRLF todoprop *alarmc "END" ":" "VTODO" CRLF todoprop = *( ; the following are REQUIRED, ; but MUST NOT occur more than once dtstamp / uid / ; the following are OPTIONAL, ; but MUST NOT occur more than once class / completed / created / description / dtstart / geo / last-mod / location / organizer / percent / priority / recurid / seq / status / summary / url / ; the following is OPTIONAL, ; but SHOULD NOT occur more than once rrule / ; either 'due' or 'duration' MAY appear in ; a 'todoprop', but 'due' and 'duration' ; MUST NOT occur in the same 'todoprop'. ; If 'duration' appear in a 'todoprop', ; then 'dtstart' MUST also appear in ' the same 'todoprop'. due / duration / ; the following are OPTIONAL, ; and MAY occur more than once attach / attendee / categories / comment / contact / exdate / rstatus / related / resources / rdate / x-prop / iana-prop ) Desruisseaux Expires September 3, 2007 [Page 53] Internet-Draft iCalendar March 2007 Description: A "VTODO" calendar component is a grouping of component properties and possibly "VALARM" calendar components that represent an action-item or assignment. For example, it can be used to represent an item of work assigned to an individual; such as "turn in travel expense today". The "VTODO" calendar component cannot be nested within another calendar component. However, "VTODO" calendar components can be related to each other or to a "VEVENT" or to a "VJOURNAL" calendar component with the "RELATED-TO" property. A "VTODO" calendar component without the "DTSTART" and "DUE" (or "DURATION") properties specifies a to-do that will be associated with each successive calendar date, until it is completed. Example: The following is an example of a "VTODO" calendar component: BEGIN:VTODO UID:19970901T130000Z-123404@example.com DTSTAMP:19970901T130000Z DTSTART:19970415T133000Z DUE:19970416T045959Z SUMMARY:1996 Income Tax Preparation CLASS:CONFIDENTIAL CATEGORIES:FAMILY,FINANCE PRIORITY:1 STATUS:NEEDS-ACTION END:VTODO 3.6.3. Journal Component Component Name: VJOURNAL Purpose: Provide a grouping of component properties that describe a journal entry. Format Definition: A "VJOURNAL" calendar component is defined by the following notation: Desruisseaux Expires September 3, 2007 [Page 54] Internet-Draft iCalendar March 2007 journalc = "BEGIN" ":" "VJOURNAL" CRLF jourprop "END" ":" "VJOURNAL" CRLF jourprop = *( ; the following are REQUIRED, ; but MUST NOT occur more than once dtstamp / uid / ; the following are OPTIONAL, ; but MUST NOT occur more than once class / created / dtstart / last-mod / organizer / recurid / seq / status / summary / url / ; the following is OPTIONAL, ; but SHOULD NOT occur more than once rrule / ; the following are OPTIONAL, ; and MAY occur more than once attach / attendee / categories / comment / contact / description / exdate / related / rdate / rstatus / x-prop / iana-prop ) Description: A "VJOURNAL" calendar component is a grouping of component properties that represent one or more descriptive text notes associated with a particular calendar date. The "DTSTART" property is used to specify the calendar date that the journal entry is associated with. Generally, it will have a DATE value data type, but it can also be used to specify a DATE-TIME value data type. Examples of a journal entry include a daily record of a legislative body or a journal entry of individual telephone contacts for the day or an ordered list of accomplishments for the day. The "VJOURNAL" calendar component can also be used to associate a document with a calendar date. The "VJOURNAL" calendar component does not take up time on a calendar. Hence, it does not play a role in free or busy time searches -- it is as though it has a time transparency value of TRANSPARENT. It is transparent to any such searches. Desruisseaux Expires September 3, 2007 [Page 55] Internet-Draft iCalendar March 2007 The "VJOURNAL" calendar component cannot be nested within another calendar component. However, "VJOURNAL" calendar components can be related to each other or to a "VEVENT" or to a "VTODO" calendar component, with the "RELATED-TO" property. Example: The following is an example of the "VJOURNAL" calendar component: BEGIN:VJOURNAL UID:19970901T130000Z-123405@example.com DTSTAMP:19970901T130000Z DTSTART;VALUE=DATE:19970317 SUMMARY:Staff meeting minutes DESCRIPTION:1. Staff meeting: Participants include Joe\, Lisa and Bob. Aurora project plans were reviewed. There is currentl y no budget reserves for this project. Lisa will escalate to management. Next meeting on Tuesday.\n 2. Telephone Conference: ABC Corp. sales representative called to discuss new printer. Promised to get us a demo by Friday.\n 3. Henry Miller (Handsoff Insurance): Car was totaled by tree. Is looking into a loaner car. 555-2323 (tel). END:VJOURNAL 3.6.4. Free/Busy Component Component Name: VFREEBUSY Purpose: Provide a grouping of component properties that describe either a request for free/busy time, describe a response to a request for free/busy time or describe a published set of busy time. Format Definition: A "VFREEBUSY" calendar component is defined by the following notation: Desruisseaux Expires September 3, 2007 [Page 56] Internet-Draft iCalendar March 2007 freebusyc = "BEGIN" ":" "VFREEBUSY" CRLF fbprop "END" ":" "VFREEBUSY" CRLF fbprop = *( ; the following are REQUIRED, ; but MUST NOT occur more than once dtstamp / uid / ; the following are OPTIONAL, ; but MUST NOT occur more than once contact / dtstart / dtend / duration / dtstamp / organizer / uid / url / ; the following are OPTIONAL, ; and MAY occur more than once attendee / comment / freebusy / rstatus / x-prop / iana-prop ) Description: A "VFREEBUSY" calendar component is a grouping of component properties that represents either a request for, a reply to a request for free or busy time information or a published set of busy time information. When used to request free/busy time information, the "ATTENDEE" property specifies the calendar users whose free/busy time is being requested; the "ORGANIZER" property specifies the calendar user who is requesting the free/busy time; the "DTSTART" and "DTEND" properties specify the window of time for which the free/ busy time is being requested; the "UID" and "DTSTAMP" properties are specified to assist in proper sequencing of multiple free/busy time requests. When used to reply to a request for free/busy time, the "ATTENDEE" property specifies the calendar user responding to the free/busy time request; the "ORGANIZER" property specifies the calendar user that originally requested the free/busy time; the "FREEBUSY" property specifies the free/busy time information (if it exists); and the "UID" and "DTSTAMP" properties are specified to assist in proper sequencing of multiple free/busy time replies. Desruisseaux Expires September 3, 2007 [Page 57] Internet-Draft iCalendar March 2007 When used to publish busy time, the "ORGANIZER" property specifies the calendar user associated with the published busy time; the "DTSTART" and "DTEND" properties specify an inclusive time window that surrounds the busy time information; the "FREEBUSY" property specifies the published busy time information; and the "DTSTAMP" property specifies the date/time that iCalendar object was created. The "VFREEBUSY" calendar component cannot be nested within another calendar component. Multiple "VFREEBUSY" calendar components can be specified within an iCalendar object. This permits the grouping of Free/Busy information into logical collections, such as monthly groups of busy time information. The "VFREEBUSY" calendar component is intended for use in iCalendar object methods involving requests for free time, requests for busy time, requests for both free and busy, and the associated replies. Free/Busy information is represented with the "FREEBUSY" property. This property provides a terse representation of time periods. One or more "FREEBUSY" properties can be specified in the "VFREEBUSY" calendar component. When present in a "VFREEBUSY" calendar component, the "DTSTART" and "DTEND" properties SHOULD be specified prior to any "FREEBUSY" properties. In a free time request, these properties can be used in combination with the "DURATION" property to represent a request for a duration of free time within a specified window of time. The recurrence properties ("RRULE", "RDATE", "EXDATE") are not permitted within a "VFREEBUSY" calendar component. Any recurring events are resolved into their individual busy time periods using the "FREEBUSY" property. Example: The following is an example of a "VFREEBUSY" calendar component used to request free or busy time information: BEGIN:VFREEBUSY UID:19970901T082949Z-FA43EF@example.com ORGANIZER:mailto:jane_doe@example.com ATTENDEE:mailto:john_public@example.com DTSTART:19971015T050000Z DTEND:19971016T050000Z DTSTAMP:19970901T083000Z END:VFREEBUSY Desruisseaux Expires September 3, 2007 [Page 58] Internet-Draft iCalendar March 2007 The following is an example of a "VFREEBUSY" calendar component used to reply to the request with busy time information: BEGIN:VFREEBUSY UID:19970901T095957Z-76A912@example.com ORGANIZER:mailto:jane_doe@example.com ATTENDEE:mailto:john_public@example.com DTSTAMP:19970901T100000Z FREEBUSY:19971015T050000Z/PT8H30M, 19971015T160000Z/PT5H30M,19971015T223000Z/PT6H30M URL:http://example.com/pub/busy/jpublic-01.ifb COMMENT:This iCalendar file contains busy time information for the next three months. END:VFREEBUSY The following is an example of a "VFREEBUSY" calendar component used to publish busy time information. BEGIN:VFREEBUSY UID:19970901T115957Z-76A912@example.com DTSTAMP:19970901T120000Z ORGANIZER:jsmith@example.com DTSTART:19980313T141711Z DTEND:19980410T141711Z FREEBUSY:19980314T233000Z/19980315T003000Z FREEBUSY:19980316T153000Z/19980316T163000Z FREEBUSY:19980318T030000Z/19980318T040000Z URL:http://www.example.com/calendar/busytime/jsmith.ifb END:VFREEBUSY 3.6.5. Time Zone Component Component Name: VTIMEZONE Purpose: Provide a grouping of component properties that defines a time zone. Format Definition: A "VTIMEZONE" calendar component is defined by the following notation: timezonec = "BEGIN" ":" "VTIMEZONE" CRLF *( ; 'tzid' is REQUIRED, but MUST NOT occur more ; than once tzid / Desruisseaux Expires September 3, 2007 [Page 59] Internet-Draft iCalendar March 2007 ; 'last-mod' and 'tzurl' are OPTIONAL, ; but MUST NOT occur more than once last-mod / tzurl / ; one of 'standardc' or 'daylightc' MUST occur ; and each MAY occur more than once. standardc / daylightc / ; the following are OPTIONAL, ; and MAY occur more than once x-prop / iana-prop ) "END" ":" "VTIMEZONE" CRLF standardc = "BEGIN" ":" "STANDARD" CRLF tzprop "END" ":" "STANDARD" CRLF daylightc = "BEGIN" ":" "DAYLIGHT" CRLF tzprop "END" ":" "DAYLIGHT" CRLF tzprop = *( ; the following are REQUIRED, ; but MUST NOT occur more than once dtstart / tzoffsetto / tzoffsetfrom / ; the following is OPTIONAL, ; but SHOULD NOT occur more than once rrule / ; the following are OPTIONAL, ; and MAY occur more than once comment / rdate / tzname / x-prop / iana-prop ) Desruisseaux Expires September 3, 2007 [Page 60] Internet-Draft iCalendar March 2007 Description: A time zone is unambiguously defined by the set of time measurement rules determined by the governing body for a given geographic area. These rules describe at a minimum the base offset from UTC for the time zone, often referred to as the Standard Time offset. Many locations adjust their Standard Time forward or backward by one hour, in order to accommodate seasonal changes in number of daylight hours, often referred to as Daylight Saving Time. Some locations adjust their time by a fraction of an hour. Standard Time is also known as Winter Time. Daylight Saving Time is also known as Advanced Time, Summer Time, or Legal Time in certain countries. The following table shows the changes in time zone rules in effect for New York City starting from 1967. Each line represents a description or rule for a particular observance. Effective Observance Rule +-----------+--------------------------+--------+--------------+ | Date | (Date/Time) | Offset | Abbreviation | +-----------+--------------------------+--------+--------------+ | 1967-2006 | last Sun in Oct, 02:00 | -0500 | EST | | 1967-1973 | last Sun in Apr, 02:00 | -0400 | EDT | | 1974-1974 | Jan 6, 02:00 | -0400 | EDT | | 1975-1975 | Feb 23, 02:00 | -0400 | EDT | | 1976-1986 | last Sun in Apr, 02:00 | -0400 | EDT | | 1987-2006 | first Sun in Apr, 02:00 | -0400 | EDT | | 2007-* | first Sun in Nov, 02:00 | -0500 | EST | | 2007-* | second Sun in Mar, 02:00 | -0400 | EDT | +-----------+--------------------------+--------+--------------+ Note: The specification of a global time zone registry is not addressed by this document and is left for future study. However, implementers may find the TZ database [TZDB] a useful reference. It is an informal, public-domain collection of time zone information, which is currently being maintained by volunteer Internet participants, and is used in several operating systems. This database contains current and historical time zone information for a wide variety of locations around the globe; it provides a time zone identifier for every unique time zone rule set in actual use since 1970, with historical data going back to the introduction of standard time. Interoperability between two calendaring and scheduling applications, especially for recurring events, to-dos or journal entries, is dependent on the ability to capture and convey date and time information in an unambiguous format. The specification of current time zone information is integral to this behavior. Desruisseaux Expires September 3, 2007 [Page 61] Internet-Draft iCalendar March 2007 If present, the "VTIMEZONE" calendar component defines the set of Standard Time and Daylight Saving Time observances (or rules) for a particular time zone for a given interval of time. The "VTIMEZONE" calendar component cannot be nested within other calendar components. Multiple "VTIMEZONE" calendar components can exist in an iCalendar object. In this situation, each "VTIMEZONE" MUST represent a unique time zone definition. This is necessary for some classes of events, such as airline flights, that start in one time zone and end in another. The "VTIMEZONE" calendar component MUST include the "TZID" property and at least one definition o