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RFC 5545

 
 
 

Internet Calendaring and Scheduling Core Object Specification (iCalendar)

Part 2 of 7, p. 13 to 50
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3.2.  Property Parameters

   A property can have attributes with which it is associated.  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, SEMICOLON, or COMMA
   character separators MUST be specified as quoted-string text values.
   Property parameter values MUST NOT contain the DQUOTE character.  The
   DQUOTE character is used as a delimiter for parameter values that
   contain restricted characters or URI text.  For example:

     DESCRIPTION;ALTREP="cid:part1.0001@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:

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     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
                   / rangeparam        ; Recurrence identifier range
                   / 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.

   Applications MUST ignore x-param and iana-param values they don't
   recognize.

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

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      the default representation of the text value.  The URI parameter
      value MUST be specified in a quoted-string.

         Note: While there is no restriction imposed on the URI schemes
         allowed for this parameter, Content Identifier (CID) [RFC2392],
         HTTP [RFC2616], and HTTPS [RFC2818] are the URI schemes most
         commonly used by current implementations.

   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:<part3.msg.970415T083000@example.com>

       <html>
         <head>
          <title></title>
         </head>
         <body>
           <p>
             <b>Project XYZ Review Meeting</b> will include
             the following agenda items:
             <ol>
               <li>Market Overview</li>
               <li>Finances</li>
               <li>Project Management</li>
             </ol>
           </p>
         </body>
       </html>

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:

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     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.

   Example:

       ORGANIZER;CN="John Smith":mailto:jsmith@example.com

3.2.3.  Calendar User Type

   Parameter Name:  CUTYPE

   Purpose:  To identify 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.
      Applications MUST treat x-name and iana-token values they don't
      recognize the same way as they would the UNKNOWN value.

   Example:

       ATTENDEE;CUTYPE=GROUP:mailto:ietf-calsch@example.org

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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)

   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 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 individual calendar address parameter values MUST each be
      specified in a quoted-string.

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   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.

   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.

         Note: While there is no restriction imposed on the URI schemes
         allowed for this parameter, CID [RFC2392], DATA [RFC2397], FILE
         [RFC1738], FTP [RFC1738], HTTP [RFC2616], HTTPS [RFC2818], LDAP
         [RFC4516], and MID [RFC2392] are the URI schemes most commonly
         used by current implementations.

   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:

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       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;FMTTYPE=text/plain;ENCODING=BASE64;VALUE=BINARY:TG9yZW
      0gaXBzdW0gZG9sb3Igc2l0IGFtZXQsIGNvbnNlY3RldHVyIGFkaXBpc2ljaW
      5nIGVsaXQsIHNlZCBkbyBlaXVzbW9kIHRlbXBvciBpbmNpZGlkdW50IHV0IG
      xhYm9yZSBldCBkb2xvcmUgbWFnbmEgYWxpcXVhLiBVdCBlbmltIGFkIG1pbm
      ltIHZlbmlhbSwgcXVpcyBub3N0cnVkIGV4ZXJjaXRhdGlvbiB1bGxhbWNvIG
      xhYm9yaXMgbmlzaSB1dCBhbGlxdWlwIGV4IGVhIGNvbW1vZG8gY29uc2VxdW
      F0LiBEdWlzIGF1dGUgaXJ1cmUgZG9sb3IgaW4gcmVwcmVoZW5kZXJpdCBpbi
      B2b2x1cHRhdGUgdmVsaXQgZXNzZSBjaWxsdW0gZG9sb3JlIGV1IGZ1Z2lhdC
      BudWxsYSBwYXJpYXR1ci4gRXhjZXB0ZXVyIHNpbnQgb2NjYWVjYXQgY3VwaW
      RhdGF0IG5vbiBwcm9pZGVudCwgc3VudCBpbiBjdWxwYSBxdWkgb2ZmaWNpYS
      BkZXNlcnVudCBtb2xsaXQgYW5pbSBpZCBlc3QgbGFib3J1bS4=

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-name "/" subtype-name
                      ; Where "type-name" and "subtype-name" are
                      ; defined in Section 4.2 of [RFC4288].

   Description:  This parameter can be specified on properties that are
      used to reference an object.  The parameter specifies the media
      type [RFC4288] of the referenced object.  For example, on the
      "ATTACH" property, an FTP type URI value does not, by itself,

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      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.

   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.  Applications MUST treat x-name
      and iana-token values they don't recognize the same way as they
      would the BUSY value.

   Example:  The following is an example of this parameter on a
      "FREEBUSY" property.

       FREEBUSY;FBTYPE=BUSY:19980415T133000Z/19980415T170000Z

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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 [RFC5646].

   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 [RFC5646].

      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=en-US:Company Holiday Party

       LOCATION;LANGUAGE=en:Germany

       LOCATION;LANGUAGE=no:Tyskland

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)

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   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-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:

       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

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                        / "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
      "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.
      Applications MUST treat x-name and iana-token values they don't
      recognize the same way as they would the NEEDS-ACTION value.

   Example:

       ATTENDEE;PARTSTAT=DECLINED:mailto:jsmith@example.com

3.2.13.  Recurrence Identifier Range

   Parameter Name:  RANGE

   Purpose:  To specify the effective range of recurrence instances from
      the instance specified by the recurrence identifier specified by
      the property.

   Format Definition:  This property parameter is defined by the
      following notation:

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       rangeparam = "RANGE" "=" "THISANDFUTURE"
       ; To specify the instance specified by the recurrence identifier
       ; and all subsequent recurrence instances.

   Description:  This parameter can be specified on a property that
      specifies a recurrence identifier.  The parameter specifies the
      effective range of recurrence instances that is specified by the
      property.  The effective range is from the recurrence identifier
      specified by the property.  If this parameter is not specified on
      an allowed property, then the default range is the single instance
      specified by the recurrence identifier value of the property.  The
      parameter value can only be "THISANDFUTURE" to indicate a range
      defined by the recurrence identifier and all subsequent instances.
      The value "THISANDPRIOR" is deprecated by this revision of
      iCalendar and MUST NOT be generated by applications.

   Example:

       RECURRENCE-ID;RANGE=THISANDFUTURE:19980401T133000Z

3.2.14.  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

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3.2.15.  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:

       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; or 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.
      Applications MUST treat x-name and iana-token values they don't
      recognize the same way as they would the PARENT value.

   Example:

       RELATED-TO;RELTYPE=SIBLING:19960401-080045-4000F192713@
        example.com

3.2.16.  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:

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       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

   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.
      Applications MUST treat x-name and iana-token values they don't
      recognize the same way as they would the REQ-PARTICIPANT value.

   Example:

       ATTENDEE;ROLE=CHAIR:mailto:mrbig@example.com

3.2.17.  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.

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   Example:

       ATTENDEE;RSVP=TRUE:mailto:jsmith@example.com

3.2.18.  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

   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

3.2.19.  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
      neither 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

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      that 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.
      Failure to include and follow VTIMEZONE definitions in iCalendar
      objects may lead to inconsistent understanding of the local time
      at any given location.

      The presence of the SOLIDUS character as a prefix, indicates that
      this "TZID" represents a unique ID in a globally defined time zone
      registry (when such registry is defined).

         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
      properties and 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 floating time,
      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.

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3.2.20.  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:

       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.

      Applications MUST preserve the value data for x-name and iana-
      token values that they don't recognize without attempting to
      interpret or parse the value data.

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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

   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, see Section 3.3.11) is defined for this value type.

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   Example:  The following is an example of a "BASE64" encoded binary
      value data:

     ATTACH;FMTTYPE=image/vnd.microsoft.icon;ENCODING=BASE64;VALUE
      =BINARY:AAABAAEAEBAQAAEABAAoAQAAFgAAACgAAAAQAAAAIAAAAAEABAAA
      AAAAAAAAAAAAAAAAAAAAAAAAAAAAAACAAAAAgIAAAICAgADAwMAA////AAAA
      AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
      AAAAAAAAAAAAAAAAAAAAAAMwAAAAAAABNEMQAAAAAAAkQgAAAAAAJEREQgAA
      ACECQ0QgEgAAQxQzM0E0AABERCRCREQAADRDJEJEQwAAAhA0QwEQAAAAAERE
      AAAAAAAAREQAAAAAAAAkQgAAAAAAAAMgAAAAAAAAAAAAAAAAAAAAAAAAAAAA
      AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
      AAAAAAAAAAAA

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, see
      Section 3.3.11) is defined for this value type.

   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

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      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, see Section 3.3.11)
      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

   Description:  If the property permits, multiple "date" values are
      specified as a COMMA-separated list of values.  The format for the
      value type is based on the [ISO.8601.2004] 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, see Section 3.3.11) 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.

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   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-separated list of values.  No additional
      content value encoding (i.e., BACKSLASH character encoding, see
      Section 3.3.11) 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.8601.2004] 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,
      the 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

      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

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      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, 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.

      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 3.2.19.  For example, the following represents
      2:00 A.M. in New York on January 19, 1998:

       TZID=America/New_York:19980119T020000

      If, based on the definition of the referenced time zone, the local
      time described occurs more than once (when changing from daylight
      to standard time), the DATE-TIME value refers to the first
      occurrence of the referenced time.  Thus, TZID=America/
      New_York:20071104T013000 indicates November 4, 2007 at 1:30 A.M.
      EDT (UTC-04:00).  If the local time described does not occur (when
      changing from standard to daylight time), the DATE-TIME value is
      interpreted using the UTC offset before the gap in local times.
      Thus, TZID=America/New_York:20070311T023000 indicates March 11,
      2007 at 3:30 A.M. EDT (UTC-04:00), one hour after 1:30 A.M. EST
      (UTC-05:00).

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      A time value MUST only specify the second 60 when specifying a
      positive leap second.  For example:

       19970630T235960Z

      Implementations that do not support leap seconds SHOULD interpret
      the second 60 as equivalent to the second 59.

   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

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"

   Description:  If the property permits, multiple "duration" values are
      specified by a COMMA-separated list of values.  The format is
      based on the [ISO.8601.2004] complete representation basic format
      with designators for the duration of time.  The format can
      represent nominal durations (weeks and days) and accurate
      durations (hours, minutes, and seconds).  Note that unlike
      [ISO.8601.2004], this value type doesn't support the "Y" and "M"
      designators to specify durations in terms of years and months.

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      The duration of a week or a day depends on its position in the
      calendar.  In the case of discontinuities in the time scale, such
      as the change from standard time to daylight time and back, the
      computation of the exact duration requires the subtraction or
      addition of the change of duration of the discontinuity.  Leap
      seconds MUST NOT be considered when computing an exact duration.
      When computing an exact duration, the greatest order time
      components MUST be added first, that is, the number of days MUST
      be added first, followed by the number of hours, number of
      minutes, and number of 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, see Section 3.3.11) 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-separated list of values.

      No additional content value encoding (i.e., BACKSLASH character
      encoding, see Section 3.3.11) is defined for this value type.

   Example:

       1000000.0000001
       1.333
       -3.14

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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-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, see Section 3.3.11) 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.8601.2004] 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.8601.2004] complete representation basic format for a
       ; period of time consisting of a start and positive duration
       ; of time.

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   Description:  If the property permits, multiple "period" values are
      specified by a COMMA-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 based on the
      [ISO.8601.2004] complete representation, basic format for "DATE-
      TIME" start of the period, followed by a SOLIDUS character
      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 based on the [ISO.8601.2004]
      complete representation, basic format for the "DATE-TIME" start of
      the period, followed by a SOLIDUS character, followed by the
      [ISO.8601.2004] 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, see Section 3.3.11) 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.
                       ;
                       ; The UNTIL or COUNT rule parts are OPTIONAL,
                       ; but they MUST NOT occur in the same 'recur'.
                       ;

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                       ; 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

       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

       weekday     = "SU" / "MO" / "TU" / "WE" / "TH" / "FR" / "SA"
       ;Corresponding to SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY,
       ;FRIDAY, and SATURDAY days of the week.

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       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.  The rule parts are not
      ordered in any particular sequence.  Individual rule parts MUST
      only be specified once.  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
      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.

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      The INTERVAL rule part contains a positive integer representing at
      which intervals the recurrence rule repeats.  The default value is
      "1", meaning every second for a SECONDLY rule, 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.  For example,
      within a DAILY rule, a value of "8" means every eight days.

      The UNTIL rule part defines a DATE or DATE-TIME value that 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.  Furthermore, if the
      "DTSTART" property is specified as a date with local time, then
      the UNTIL rule part MUST also be specified as a date with local
      time.  If the "DTSTART" property is specified as a date with UTC
      time or a date with local time and time zone reference, then the
      UNTIL rule part MUST be specified as a date with UTC time.  In the
      case of the "STANDARD" and "DAYLIGHT" sub-components the UNTIL
      rule part MUST always be specified as a date with UTC time.  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-separated list of seconds
      within a minute.  Valid values are 0 to 60.  The BYMINUTE rule
      part specifies a COMMA-separated list of minutes within an hour.
      Valid values are 0 to 59.  The BYHOUR rule part specifies a COMMA-
      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-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; and 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 a specific day within the MONTHLY or YEARLY "RRULE".

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      For example, within a MONTHLY rule, +1MO (or simply 1MO)
      represents the first Monday within the month, whereas -1MO
      represents the last Monday of the month.  The numeric value in a
      BYDAY rule part with the FREQ rule part set to YEARLY corresponds
      to an offset within the month when the BYMONTH rule part is
      present, and corresponds to an offset within the year when the
      BYWEEKNO or BYMONTH rule parts are present.  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 BYDAY rule part MUST
      NOT be specified with a numeric value when the FREQ rule part is
      not set to MONTHLY or YEARLY.  Furthermore, the BYDAY rule part
      MUST NOT be specified with a numeric value with the FREQ rule part
      set to YEARLY when the BYWEEKNO rule part is specified.

      The BYMONTHDAY rule part specifies a COMMA-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 BYMONTHDAY rule part MUST NOT be specified when the FREQ rule
      part is set to WEEKLY.

      The BYYEARDAY rule part specifies a COMMA-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 BYYEARDAY rule part MUST NOT be specified when the FREQ
      rule part is set to DAILY, WEEKLY, or MONTHLY.

      The BYWEEKNO rule part specifies a COMMA-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.8601.2004].  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 that contains at least four (4) days in that
      calendar year.  This rule part MUST NOT be used when the FREQ rule
      part is set to anything other than YEARLY.  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-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

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      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-separated list of values
      that corresponds to the nth occurrence within the set of
      recurrence instances specified by the rule.  BYSETPOS operates on
      a set of recurrence instances in one interval of the recurrence
      rule.  For example, in a WEEKLY rule, the interval would be one
      week A set of recurrence instances starts at the beginning of the
      interval defined by the FREQ rule part.  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 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 occurrences specified by the
      rule.

      Recurrence rules may generate recurrence instances with an 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 that 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.

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      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.

      The table below summarizes the dependency of BYxxx rule part
      expand or limit behavior on the FREQ rule part value.

      The term "N/A" means that the corresponding BYxxx rule part MUST
      NOT be used with the corresponding FREQ value.

      BYDAY has some special behavior depending on the FREQ value and
      this is described in separate notes below the table.

   +----------+--------+--------+-------+-------+------+-------+------+
   |          |SECONDLY|MINUTELY|HOURLY |DAILY  |WEEKLY|MONTHLY|YEARLY|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYMONTH   |Limit   |Limit   |Limit  |Limit  |Limit |Limit  |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYWEEKNO  |N/A     |N/A     |N/A    |N/A    |N/A   |N/A    |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYYEARDAY |Limit   |Limit   |Limit  |N/A    |N/A   |N/A    |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYMONTHDAY|Limit   |Limit   |Limit  |Limit  |N/A   |Expand |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYDAY     |Limit   |Limit   |Limit  |Limit  |Expand|Note 1 |Note 2|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYHOUR    |Limit   |Limit   |Limit  |Expand |Expand|Expand |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYMINUTE  |Limit   |Limit   |Expand |Expand |Expand|Expand |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYSECOND  |Limit   |Expand  |Expand |Expand |Expand|Expand |Expand|
   +----------+--------+--------+-------+-------+------+-------+------+
   |BYSETPOS  |Limit   |Limit   |Limit  |Limit  |Limit |Limit  |Limit |
   +----------+--------+--------+-------+-------+------+-------+------+

      Note 1:  Limit if BYMONTHDAY is present; otherwise, special expand
               for MONTHLY.

      Note 2:  Limit if BYYEARDAY or BYMONTHDAY is present; otherwise,
               special expand for WEEKLY if BYWEEKNO present; otherwise,
               special expand for MONTHLY if BYMONTH present; otherwise,
               special expand for YEARLY.

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      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
      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.

      If the computed local start time of a recurrence instance does not
      exist, or occurs more than once, for the specified time zone, the
      time of the recurrence instance is interpreted in the same manner
      as an explicit DATE-TIME value describing that date and time, as
      specified in Section 3.3.5.

      No additional content value encoding (i.e., BACKSLASH character
      encoding, see Section 3.3.11) is defined for this value type.

   Example:  The following is a rule that specifies 10 occurrences that
      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:

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       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 = WSP / %x21 / %x23-2B / %x2D-39 / %x3C-5B /
                    %x5D-7E / NON-US-ASCII
          ; Any character except CONTROLs not needed by the current
          ; character set, DQUOTE, ";", ":", "\", ","

   Description:  If the property permits, multiple TEXT values are
      specified by a COMMA-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, followed by a LATIN SMALL LETTER
      N or a LATIN CAPITAL LETTER N, 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 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.  A SEMICOLON character in a "TEXT" property value MUST
      be escaped with a BACKSLASH character.  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.

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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:

       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-separated list of values.  No additional
      content value encoding (i.e., BACKSLASH character encoding, see
      Section 3.3.11) 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.8601.2004] 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

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      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", 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 floating time, 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, 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 3.2.19.

   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

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3.3.13.  URI

   Value Name:  URI

   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 = <As defined in Section 3 of [RFC3986]>

   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, see Section 3.3.11) 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 character MUST be specified for positive
      UTC offsets (i.e., ahead of UTC).  The HYPHEN-MINUS character MUST
      be specified for negative UTC offsets (i.e., behind of UTC).  The

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      value of "-0000" and "-000000" are not allowed.  The time-second,
      if present, MUST NOT be 60; if absent, it defaults to zero.

      No additional content value encoding (i.e., BACKSLASH character
      encoding, see Section 3.3.11) 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



(page 50 continued on part 3)

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