Foreword

This document updates the following specifications:

• I-D.calconnect-vobject-vformat, The vObject Model and vFormat Syntax

• RFC 6350, vCard version 4.0

• RFC 5545, Internet Calendaring and Scheduling Core Object Specification (iCalendar)

• RFC 7953, Calendar Availability Extensions

This work is produced by the CalConnect TC-VCARD and TC-CALENDAR committees.

1.  Scope

Methods described in this document are intended to be used by vObject-compliant standards, such as vCard 4.0 RFC 6350 and iCalendar RFC 5545.

2.  Normative references

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

IETF RFC 5545, Internet Calendaring and Scheduling Core Object Specification (iCalendar)

IETF RFC 6350, vCard Format Specification

IETF I-D.calconnect-vobject-vformat, The vObject Model and vFormat Syntax

3.  Terms and definitions

For the purposes of this document, the following terms and definitions apply.

3.1. 

General

The key words “MUST“, “MUST NOT“, “REQUIRED“, “SHALL“, “SHALL NOT“, “SHOULD“, “SHOULD NOT“, “RECOMMENDED“, “NOT RECOMMENDED“, “MAY“, and “OPTIONAL” in this document are to be interpreted as described in BCP 14 RFC 2119 RFC 8174 when, and only when, they appear in all capitals, as shown here.

The key words “Private Use“, “Experimental Use“, “Hierarchical Allocation“, “First Come First Served“, “Expert Review“, “Specification Required“, “RFC Required“, “IETF Review“, “Standards Action” and “IESG Approval” in this document are to be interpreted as described in 4.

Notation in this document is described in ABNF RFC 5234 as used by RFC 6350.

Definitions from RFC 6350 apply to this specification except when explicitly overridden.

All names of properties, property parameters, enumerated property values, and property parameter values are case-insensitive. However, all property values are case-sensitive, unless otherwise stated.

4.  Property Parameter Usage Clarification: LANGUAGE

This section clarifies the intent of the LANGUAGE property parameter in RFC 5545 and RFC 6350 to be for the identification of the language used in the property value where the parameter is specified.

The RFC 5646 defined language-tag allows specification of multiple attributes (called “subtags”) in addition to just language. Its basic form includes:

• a mandatory language subtag, using a language identifier from ISO 639 (-2, -3) (called a “primary” or “extended” language subtag)

• an optional script subtag, using a script identifier from ISO 15924

• an optional region subtag, using country codes listed in ISO 3166 or a UN numeric code

• one or more, optional, variant and extension subtags defined in the IANA language subtag registry.

In practical usage of vObject standards, including RFC 5545 and RFC 6350, it is determined that the combinatorial enumeration of non-language subtags often cause unnecessary confusion in interpretation and parsing, especially when the registry contain variant and extension subtags that either conflict in semantics or have overly restrictive in their supported prefixes.

This document therefore clarifies the intent of 3.2.10 and 5.1, such that the LANGUAGE property parameter SHOULD only support the mandatory language subtag.

Other subtags MAY be supplied as specified in RFC 5646, but they are purely for informational purposes not used in the vObject specification.

Namespace

Property parameter name

LANGUAGE

Purpose

To specify the language used in the property value.

Value type

LANGUAGE-TAG 4.8

Description

As provided above.

languageparam = "LANGUAGE" "=" language *(subpart)

language = iso-639-3-code / iso-639-2-code
          ; a 2-alpha or 3-alpha language code
          ; defined in ISO 639

subpart  = "-" *alphanum
           ; all other subparts unsupported

N;LANGUAGE=en:Miyazaki;Hayao;;;
N;LANGUAGE=jp:宮崎;駿;;;

5.  Property Parameter: SCRIPT

The SCRIPT property parameter specifies the written script used in the property value which contains the parameter, which is amongst the valid codes in the ISO 15924 registry.

It is separated from the LANGUAGE property parameter defined in RFC 5545 and RFC 6350 for reasons stated in Clause 4.

Namespace

Property parameter name

SCRIPT

Purpose

To specify the script used in the property value, which is amongst the valid codes in the ISO 15924 registry.

Value type

TEXT, a single value valid in the ISO 15924 script registry.

Description

The property value of which this property parameter applies to must have identical structure to

scriptparam = "SCRIPT" "=" script-code
            ; script-code defined in the value type SCRIPT-CODE

N;SCRIPT=Hira;LANGUAGE=jp:みやざき;はやお;;;
N;SCRIPT=Hani;LANGUAGE=jp:宮崎;駿;;;

6.  Property Parameter: PHONETIC

A number of contact managers have long used “X-properties” to to store phonetic information of a vCard’s subject, such as X-PHONETIC-NAME, X-PHONETIC-FIRST-NAME and X-PHONETIC-LAST-NAME.

However, this is an issue for multiple reasons:

• The value of the X-property does not define the phonetic system used for its transcription;

• This X-property usage does not enable interoperability since it does not require specification of the language transcribed, as well as the script of the resulting transcription;

• The scheme of using X-properties does not allow representation of phonetics on other vCard values.

This section defines three property parameters used to store pronunciation information of a property value:

1. The script used in the pronunciation system;

2. An identifier of the pronunciation system used;

3. The source language that was transcribed by the pronunciation system.

The PHONETIC property parameter specifies the phonetic system used in the transcription of the property value, identified by the phonetic system code from the ISO XXXXX phonetic system registry.

This property parameter is often applied together with the LANGUAGE (Clause 4) and SCRIPT (Clause 5) property parameters.

Namespace

Property parameter name

PHONETIC

Purpose

To specify the phonetic system used in the property value, which is amongst the valid codes in the ISO XXXXX registry.

Value type

TEXT, a single value valid in the ISO XXXXX phonetic system registry.

Description

The property value of which this property parameter applies to must take an identical structure to the property value without application of this property parameter.

phoneticparam = "PHONETIC" "=" phonetic
phonetic      = 4ALPHA  ; ISO XXXXX 4-digit phonetic system code

N;SCRIPT=Hant;LANGUAGE=zho:孫;中山;文,逸仙;;
N;SCRIPT=Hans;LANGUAGE=zho:孙;中山;文,逸仙;;
N;PHONETIC=jyut;SCRIPT=Latn;LANGUAGE=yue:syun1;zung1saan1;man4,jat6sin1;;
N;PHONETIC=ping;SCRIPT=Latn;LANGUAGE=cmn:sun;zhongshan;rixian;;

7.  Security Considerations

Security considerations of the vObject formats themselves MUST be adhered to, including:

• vCard: RFC 6350

• iCalendar: RFC 5545, RFC 4791

• vObject: [I-D.calconnect-vobject-vformat-03]

vObject formats, especially for calendaring, scheduling and contact exchange, often involve privacy-sensitive information. Internationalization features defined in this document MAY pose risk of exposing private information if interchanged through unprotected communication channels.

Mechanisms used for the transmission of such information should implement security measures to protect against possible threats, such as eavesdropping, replay, message insertion, deletion, modification, and man-in-the-middle attacks.

8.  IANA Considerations

IANA is requested to register the following property parameters and value types in the corresponding iCalendar and vCard registries.

script-code = 4ALPHA
            ; ISO 15924 4-digit script code

phonetic-code = 4ALPHA
              ; ISO XXXXX 4-digit script code

Bibliography

[1]  CalConnect TC VCARD, CalConnect VCARD Technical Committee

[2]  CalConnect TC CALENDAR, CalConnect CALENDAR Technical Committee

[3]  ISO 5127 (all parts), Information and documentation – Foundation and vocabulary

[4]  ISO 24624:2016, Language resource management – Transcription of spoken language

[5]  IETF RFC 2119, Key words for use in RFCs to Indicate Requirement Levels

[6]  IETF RFC 3986, Uniform Resource Identifier (URI): Generic Syntax

[7]  IETF RFC 5646, Tags for Identifying Languages

[8]  IETF RFC 8174, Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words

[9]  IETF RFC 6321, xCal: The XML Format for iCalendar

[10]  IETF RFC 7265, jCal: The JSON Format for iCalendar

[11]  IETF RFC 7095, jCard: The JSON Format for vCard

[12]  IETF RFC 6352, CardDAV: vCard Extensions to Web Distributed Authoring and Versioning (WebDAV)

[13]  IETF RFC 6351, xCard: vCard XML Representation

[14]  IETF RFC 4791, Calendaring Extensions to WebDAV (CalDAV)

[15]  IETF RFC 5234, Augmented BNF for Syntax Specifications: ABNF

[16]  IETF RFC 8126, Guidelines for Writing an IANA Considerations Section in RFCs