Internet Draft                                          Paul Hoffman
draft-hoffman-i18n-terms-02.txt                           IMC & VPNC
July 18, 2001
Expires in six months

          Terminology Used in Internationalization in the IETF

Status of this memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.

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Abstract

This document provides a glossary of terms used in the IETF when
discussing internationalization. The purpose is to help frame
discussions of internationalization in the various areas of the IETF and
to help introduce the main concepts to IETF participants.


1. Introduction

As [RFC2277] summarizes: "Internationalization is for humans. This means
that protocols are not subject to internationalization; text strings
are." Many protocols throughout the IETF use text strings that are
entered by, or are visible to, humans. It should be possible for anyone
can enter or read these text strings, which means that the text must be
able to be entered in typical input methods and displayed in any human
language. This is the challenge of internationalization.

1.1 About this document

Internationalization is discussed in many working groups of the IETF.
However, few working groups have internationalization experts. When
designing or updating protocols, the question often comes up "should we
internationalize this" (or, more likely, "do we have to internationalize
this").

This document gives an overview of internationalization as it applies to
IETF standards work by covering lightly the many aspects of
internationalization and the vocabulary associated with those topics. It
is not meant to be a complete description of internationalization. The
definitions in this document are not normative for IETF standards;
however, they are useful and standards may make non-nomative reference
to this document after it becomes an RFC. Some of the definitions in
this document come from many earlier IETF documents and books.

As in many fields, there is disagreement in the internationalization
community on definitions for many words. The topic of language brings up
particularly passionate opinions for experts and non-experts alike. This
document attempts to define terms that will be most useful to the IETF
audience.

This document uses definitions from many documents that have been
developed outside the IETF. The primary documents used are:
- ISO/IEC 10646 [ISOIEC10646]
- The Unicode Standard [UNICODE]
- W3C Character Model [CHARMOD]
- IETF RFCs, including [RFC2277]

In the body of this document, the source for the definition is shown in
angle brackets, such as <ISOIEC10646>. Note that many definitions are
shown as <NONE>, which means that the definitions were crafted
originally for this document.

For some terms, there is a commentary and examples after the
definitions. In those cases, the part before the angle brackets is the
definition that comes from the original source, and the part after the
angle brackets is non-definition commentary.


2. Fundamental Terms

This section covers basic topics that are needed for almost anyone who
is involved with internationalization of IETF protocols. Many terms in
this section are based on [IDN-REQ].

language

A language is a way that humans interact. The use of language occurs in
many forms, the most common of which are speech, writing, and signing.
<NONE>

Some languages have a close relationship between the written and spoken
forms, while others have a looser relationship. [RFC3066] discusses
languages in more detail.

script

A set of graphic characters used for the written form of one or more
languages. <ISOIEC10646>

Examples of scripts are Latin, Cyrillic, Greek, Arabic, and Han (the
ideographs used in writing Chinese, Japanese, and Korean). [RFC2277]
discusses scripts in detail.

It is common for internationalization novices to mix up the terms
"language" and "script".  This can be a problem in protocols that
differentiate the two. Almost all internationalized protocols deal with
scripts (the written systems), while fewer deal with languages.

A single name can mean either a language or a script; for example,
"Arabic" is both the name of a language and the name of a script. Some
scripts are used for many languages; for example, the Russian and
Bulgarian languages are written in the Cyrillic script. Some languages
can be expressed using different scripts; the Mongolian language is
written in both the Mongolian and Cyrillic scripts. Further, some
languages are normally expressed with many scripts at the same time; for
example, the Japanese language is normally expressed in the Han,
Katakana, and Hiragana scripts in a single string of text.

character

A member of a set of elements used for the organization, control, or
representation of data. <ISOIEC10646>

There are two definitions of the word "character":

- a general description of a text entity

- the encoded entity itself

When people talk about characters, they are mostly using the first
definition. Standards, however, mostly use the second definition.

A particular character is identified by its name, not by its shape. A
name may suggest a meaning, but the character may be used for
representing other meanings as well. A name may suggest a shape, but
that does not imply that just that is commonly used in print.

coded character

A character together with its coded representation. <ISOIEC10646>

coded character set

A coded character set (CCS) is a set of unambiguous rules that
establishes a character set and the relationship between the characters
of the set and their coded representation. <ISOIEC10646>

character encoding form

A character encoding form is a mapping from a character set definition
to the actual code units used to represent the data. <UNICODE>

transcoding

Transcoding is the process of converting text data from one character
encoding form to another. Transcoders work only at the level of
character encoding and do not parse the text. Note: Transcoding may
involve one-to-one, many-to-one, one-to-many or many-to-many mappings.
Because some legacy mappings are glyphic, they may not only be
many-to-many, but also discontinuous: thus XYZ may map to yxz. <CHARMOD>

character encoding scheme

A character encoding scheme (CES) is a character encoding form plus byte
serialization. There are many character encoding schemes in Unicode,
such as UTF-8 and UTF-16. <UNICODE>

Some CESs are associated with a single CCS; for example, UTF-8 [RFC2279]
applies only to ISO/IEC 10646. Other CESs, such as ISO 2022, are
associated with many CCSs.

charset

A charset is a method of mapping a sequence of octets to a sequence of
abstract characters. A charset is, in effect, a combination of one or
more CCS with a CES. Charset names are registered by the IANA according
to procedures documented in [RFC2278]. <NONE>

Many protocol definitions use the term "character set" in their
descriptions. The term "charset" is strongly preferred over the term
"character set" because "character set" has many other definitions in
other contexts and can ths be confusing.

internationalization

In the IETF, the verb "internationalize" means to add or improve the
handling of international information in a protocol. <NONE>

Many protocols that handle text only handle one script (often, the one
that contains the letters used in English text), or leaves the question
of what character set used up to local guesswork (which leads, of
course, to interoperability problems). Internationalizing such a
protocol allows the protocol to handle more scripts, hopefully all of
the ones useful to anyone in the world.

localization

A process of adapting an internationalized application platform or
application to a specific cultural environment. In localization, the
same semantics are preserved while the syntax may be changed.
[FRAMEWORK]

Localization is the act of tailoring an application for a different
language or script. Some internationalized applications can handle a
wide variety of languages. Typical users only understand a small number
of languages, so the program must be tailored to interact with users in
just the languages they know.

The major work of localization is translating the user interface and
documentation, not dealing with localization of protocols. Localization
involves not only changing the language interaction, but also other
relevant changes such as display of numbers, dates, currency, and so on.

Do not confuse "localization" with "locale", which is described later in
this document.

i18n, l10n

These are abbreviations for "internationalization" and "localization".
<NONE>

"18" is the number of characters between the "i" and the "n" in
"internationalization", and "10" is the number of characters between the
"l" and the "n" in "localization".

multilingual

The term "multilingual" has many widely-varying definitions and thus is
not recommended for use in standards. Some of the definitions relate to
the ability to handle international characters; other definitions relate
to the ability to handle multiple charsets; and still others relate to
the ability to handle multiple languages. <NONE>

displaying and rendering text

To display text, a system puts characters on a visual display device
such as a screen or a printer. To render text, a system analyzes the
character input to determine how to display the text. The terms
"display" and "render" are sometimes used interchangeably. <NONE>

Combining characters modify the display of the character (or, in some
cases, characters) that precede them. When rendering such text, the
display engine must either find the glyph in the font that represents
the base character and all of the combining characters, or it must
render the combination itself. Such rendering can be straight-forward,
but it is sometimes complicated when the combining marks interact with
each other, such as when there are two combining marks that would appear
above the same character. Formatting characters can also change the way
that a renderer would display text.

Note that text might be rendered as audio and/or tactile output, such as
in systems that have been designed for people with visual disabilities.


3. Standards Bodies and Standards

This section describes some of the standards bodies and standards that
appear in discussions of internationalization in the IETF. This is an
incomplete and possibly over-full list; listing too few bodies or
standards can be just as politically dangerous as listing too many. Note
that there are many other bodies that deal with internationalization;
however, none of them appear commonly in IETF standards work.

3.1 Standards bodies

ISO

The International Organization for Standardization has been involved
with standards for characters since before the IETF was started. ISO is
a non-governmental group made up of national bodies. ISO has many
diverse standards in the international characters area; the one that is
most used in the IETF is commonly referred to as "ISO/IEC 10646",
although its official name has more qualifications. (The IEC is
International Electrotechnical Commission). ISO/IEC 10646 describes a
CCS that covers almost all known written characters in use today.

ISO/IEC 10646 is controlled by the group known as "ISO/IEC JTC 1/SC 2
WG2", often called "WG2" for short. ISO standards go through many steps
before being finished, and years often go by between changes to ISO/IEC
10646. Information on WG2, and its work products, can be found at
<http://anubis.dkuug.dk/JTC1/SC2/WG2/>.

The standard can be purchased in both print and CD-ROM versions. It
comes in multiple parts, and is amended quite often. This leads to
difficulty in citing a specific instantiation of the standard in IETF
documents.

Unicode Consortium

The second important group for international character standards is the
Unicode Consortium. The Unicode Consortium is a trade association of
companies, governments, and other groups interested in promoting the
Unicode Standard [Unicode3]. The Unicode Standard is a CCS whose
repertoire is identical to ISO/IEC 10646. The Unicode Consortium has
added features to the base CCS which make it more useful in protocols,
such as defining attributes for each character.

The Unicode Consortium publishes addenda to the Unicode Standard as
Unicode Technical Reports. There are many types of technical reports at
various stages of maturity. The Unicode Standard and affiliated
technical reports can be found at <http://www.unicode.org/>.

World Wide Web Consortium

Commonly known as the "W3C", this group created and maintains the
standard for XML, the markup language for text that has become very
popular. XML has always been fully internationalized so that there has
never needed to be a new version to handle international text.

local and regional standards organizations

Just as there are many native CCSs and charsets, there are many local
and regional standards organizations to create and support them. Common
examples of these are ANSI (United States), and CEN/ISSS (Europe).

3.2 Encodings and transformation formats of ISO/IEC 10646

Characters in the ISO/IEC 10646 CCS can be expressed in many ways.
Encoding forms are direct addressing methods, while transformation
formats are methods for expressing encoding forms as bits on the wire.

Basic Multilingual Plane (BMP)

The BMP is the first 2^16 code points in ISO/IEC 10646. The BMP is also
called "plane 0". <NONE>

UCS-2 and UCS-4

UCS-2 and UCS-4 are the two encoding forms defined for ISO/IEC 10646.
UCS-2 addresses only the BMP. Because characters have been defined
outside of the BMP, many would consider UCS-2 to be dead. UCS-4
addresses the entire range of 2^31 code points from ISO/IEC 10646 as
32-bit values. <NONE>

UTF-8

UTF-8, a transformation format defined in [RFC2279], is the preferred
encoding for IETF protocols. Characters in the BMP are encoded as one,
two, or three octets. Characters outside the BMP are encoded as four
octets.

UTF-16, UTF-16BE, and UTF-16LE

UTF-16, UTF-16BE, and UTF-16LE, three transformation formats defined in
[RFC2781], are not required by any IETF standards, and are thus used
much less often than UTF-8. Characters in the BMP are always encoded as
two octets, and many characters outside the BMP are encoded as four
octets. The three formats differ based on the order of the octets and
the presence of a special lead-in mark.

3.3 Native CCSs and charsets

Before ISO/IEC 10646 was developed, many countries developed their own
CCSs and charsets. Many dozen of these are in common use on the Internet
today. Examples include ISO 8859-5 for Cyrillic and Shift-JIS for
Japanese scripts.

The official list of the registered charset names for use with IETF
protocols is maintained by IANA and can be found at
<http://www.iana.org/assignments/character-sets>. The list contains
preferred names and aliases.

Probably the most well-known native CCS is ASCII [US-ASCII]. This CCS is
used in numerous IETF protocols that have not yet been
internationalized.


4. Character Issues

This section contains terms and topics that are commonly used in
character handling and therefore are of concern to people
internationalizing protocols. These topics are standardized outside the
IETF.

combining character

A member of an identified subset of the coded character set of ISO/IEC
10646 intended for combination with the preceding non-combining graphic
character, or with a sequence of combining characters preceded by a
non-combining character. <ISOIEC10646>

composite sequence

A sequence of graphic characters consisting of a non-combining character
followed by one or more combining characters. A graphic symbol for a
composite sequence generally consists of the combination of the graphic
symbols of each character in the sequence. A composite sequence is not a
character and therefore is not a member of the repertoire of ISO/IEC
10646. <ISOIEC10646>

In some CCSs, some characters consist of combinations of other
characters. For example, the letter "a with acute" might be a
combination of the two characters "a" and "combining acute". The rules
for combining two or more characters are called "composition rules", and
the rules for taking apart a character into other characters is called
"decomposition rules". The results of composition is called a
"precomposed character"; the results of decomposition is called a
"decomposed character".

normalization

Normalization is the transformation of data to a normal form, for
example, to unify spelling. <UNICODE>

Note that the phrase "unify spelling" in the definition above does not
mean unifying different words with the same meaning (such as "color" and
"colour"). Instead, it means unifying different character sequences that
are intended to form the same composite characters (such as
"<a><n><combining tilde><o>" and "<a><n with tilde><o>").

The purpose of normalization is to allow two strings to be compared for
equivalence. The strings "<a><n><combining tilde><o>" and "<a><n with
tilde><o>" would be shown identically on a text display device. If a
protocol designer wants those two strings to be considered equivalent
during comparison, the protocol must include normalization.

The terms "normalization" and "canonicalization" are often used
interchangeably. Generally, they both mean to convert a string of one or
more characters into another string based on standardized rules. Some
CCSs allow multiple equivalent representations for a written string;
normalization selects one among multiple equivalent representations as a
base for reference purposes in comparing strings. In internationalized
text, these rules are usually based on decomposing combined characters
or composing characters with combining characters. [UTR15] describes the
process and many forms of normalization in detail. Normalization is
important when comparing strings to see if they are the same.

case

Case is the feature of certain alphabets where the letters have two
distinct forms. These variants, which may differ markedly in shape and
size, are called the uppercase letter (also known as capital or
majuscule) and the lowercase letter (also known as small or minuscule).
Case mapping is the association of the uppercase and lowercase forms of
a letter. <UNICODE>

There is usually (but not always) a one-to-one mapping between the same
letter in the two cases. However, there are many examples of characters
which exist in one case but for which there is no corresponding
character in the other case. Case mapping can even be dependant on
locale. Converting text to have only one case is called "case folding".

sorting and collation

Collating is the process of ordering units of textual information.
Collation is usually specific to a particular language. It is also known
as alphabetizing. <UNICODE>

Many processes have a need to order strings in a consistent sequence
(sorted). For some CCS/CES combinations, there is an obvious sort order
that can be done without reference to the linguistic meaning of the
characters: the codepoint order is sufficient. That is, the codepoint
order is also the order that a person would use in sorting the
characters. For other CCS/CES (such as the ISO 2022 family), the
codepoint order would make no sense to a person and therefore is not
useful for sorting if the results will be displayed to a person.

Codepoint order is usually not how any human educated by a local school
system expects to see strings ordered; if one orders to the expectations
of a human, one has a localized sort. Sorting to codepoint order will
seem inconsistent if the strings are not normalized before sorting
because different representations of the same character will sort
differently. This problem may be smaller with a localized sort.

code table

A code table is a table showing the characters allocated to the octets
in a code. <ISOIEC10646>

4.1 Types of characters

The following definitions of types of characters do not clearly
delineate each character into one type, nor do they allow someone to
accurately predict what types would apply to a particular character. The
definitions are useful for application designers to think about the many
(sometimes confusing) properties of text.

alphabetic

An informative Unicode property. Characters that are the primary units
of alphabets and/or syllabaries, whether combining or noncombining. This
includes composite characters that are canonical equivalents to a
combining character sequence of an alphabetic base character plus one or
more combining characters: letter diagraphs; contextual variant of
alphabetic characters; ligatures of alphabetic characters; contextual
variants of ligatures; modifier letters; letterlike symbols that are
compatibility equivalents of single alphabetic letters; and
miscellaneous letter elements. <UNICODE>

ideographic

Any symbol that primarily denotes an idea (or meaning) in contrast to a
sound (or pronunciation), for example, a symbol showing a telephone or
the Han characters used in Chinese, Japanese, and Korean. <UNICODE>

punctuation

Characters that separate units of text, such as sentences and phrases,
thus clarifying the meaning of the text. The use of punctuation marks is
not limited to prose; they are also used in mathematical and scientific
formulae, for example. <UNICODE>

symbol

A character that represents a picture or icon (as compared to one that
represents a letter or punctuation). <NONE>

Examples of symbols include characters for arrows, faces, and geometric
shapes. [UNICODE] has a property that defines characters as symbols.

nonspacing character

A character that is not a combining character but does not cause a
change in position in display. <NONE>

Examples of non-spacing characters include U+FEFF (the zero-width
no-break space), control characters such as U+0007 (bell), and
formatting characters such as U+200C (zero width non-joiner).

diacritic

A mark applied or attached to a symbol to create a new symbol that
represents a modified or new value. They can also be marks applied to a
symbol irrespective of whether it changes the value of that symbol. In
the latter case, the diacritic usually represents an independent value
(for example, an accent, tone, or some other linguistic information).
Also called diacritical mark or diacritical. <UNICODE>

control character

The 65 characters in the ranges U+0000..U+001F and U+007F..U+009F. They
are also known as control codes. <UNICODE>

formatting character

Characters that are inherently invisible but that have an effect on the
surrounding characters. <UNICODE>

Examples of formatting characters include characters for specifying the
direction of text, letter-spacing characters, and characters for
specifying joining.

compatibility character

A graphic character included as a coded character of ISO/IEC 10646
primarily for compatibility with existing coded character sets.
<ISOIEC10646>


5. User interface for internationalized text

Although the IETF does not standardize user interfaces, many protocols
make assumptions about how a user will enter or see text that is used in
the protocol. Internationalization challenges assumptions about the type
and limitations of the input and output devices that may be used with
applications that use various protocols. It is therefore useful to
consider how users typically interact with internationalized text.

input methods

An input method is a mechanism for a person to enter text into an
application. <NONE>

Text can be entered into a computer in many ways. Keyboards are by far
the most common device used, but many characters cannot be entered on
typical computer keyboards in a single stroke. Many operating systems
come with system software that lets users input characters outside the
range of what is allowed by keyboards.

For example, there are dozens of different input methods for Han
characters in Chinese, Japanese, and Korean. Some start with phonetic
input through the keyboard, while others use the number of strokes in
the character. Input methods are also needed for scripts that have many
diacritics, such as European characters that have two or three
diacritics on a single alphabetic character.

rendering rules

A rendering rule is an algorithm that a system uses to decide how to
display a string of text. <NONE>

Many scripts can be directly displayed with fonts, where each character
from an input stream can simply be copied from a font system and put on
the screen or printed page. Other scripts need rules that are based on
the input stream in order to render text for display.

Some examples of these rendering rules include:

- Scripts such as Arabic (and many others), where the form of the letter
changes depending on the adjacent letters, whether the letter is
standing alone, at the beginning of a word, in the middle of a word, or
at the end of a word. The rendering rules must choose between two or
more characters.

- Scripts such as the Indic scripts, where consonants may change their
form if they are adjacent to certain other consonants or may be
displayed in an order different from the way they are stored and
pronounced. The rendering rules must choose between two or more
characters.

- Arabic and Hebrew scripts, where the order of the characters displayed
can be changed by the bidirectional properties of the alphabetic
characters and with right-to-left and left-to-right ordering marks. The
rendering rules must choose the order that characters are displayed.

graphic symbol

A graphic symbol is the visual representation of a graphic character or
of a composite sequence. <ISOIEC10646>

glyph

A glyph is an abstract form that represents one or more glyph images.
The term "glyph" is often a synonym for glyph image, which is the
actual, concrete image of a glyph representation having been rasterized
or otherwise imaged onto some display surface. In displaying character
data, one or more glyphs may be selected to depict a particular
character. These glyphs are selected by a rendering engine during
composition and layout processing. <UNICODE>

glyph code

A glyph code is a numeric code that refers to a glyph. Usually, the
glyphs contained in a font are referenced by their glyph code. Glyph
codes are local to a particular font; that is, a different font
containing the same glyphs may use different codes. <UNICODE>

font

A font is a collection of glyphs used for the visual depiction of
character data. A font is often associated with a set of parameters (for
example, size, posture, weight, and serifness), which, when set to
particular values, generate a collection of imagable glyphs. <UNICODE>

bidirectional display

The process or result of mixing left-to-right oriented text and
right-to-left oriented text in a single line is called bidirectional
display. <UNICODE>

Most of the world's written languages are displayed left-to-right.
However, many widely-used written languages such as ones based on the
Hebrew or Arabic scripts are displayed right-to-left. Right-to-left text
often confounds protocol writers because they have to keep thinking in
terms of the order of characters in a string in memory, and that order
might be different than what they see on the screen. (Note that some
scripts in some languages are written both horizontally and vertically.)

Bidirectional text can cause even more confusion because there are
formatting characters in ISO/IEC 10646 which cause the order of display
of text to change. These formatting characters are needed so that one
can properly display right-to-left characters with left-to-right
characters at the same time without forcing the one of the strings to be
stored in reverse order.

It is common to see strings with text in both directions, such as
strings that include both text and numbers, or strings that contain a
mixture of scripts.

[Unicode3] has a long and incredibly detailed algorithm for displaying
bidirectional text.

undisplayable character

A character that has no displayable form. <NONE>

For instance, the zero-width space (U+200B) cannot be displayed because
it takes up no horizontal space. Formatting characters such as those for
setting the direction of text are also undisplayable. Note, however,
that every character in [Unicode3] has a glyph associated with it, and
that the glyphs for undisplayable characters use are enclosed in a
dashed square as an indication that the actual character is
undisplayable


6. Text in current IETF protocols

Many IETF protocols started off being fully internationalized, while
others have been internationalized as they were revised. In this
process, IETF members have seen patterns in the way that many protocols
use text. This section describes some specific protocol interactions
with text.

protocol elements

[[ No definition yet. ]] <NONE>

Almost every protocol has named elements, such as "source port" in TCP.
In some protocols, the names of the elements (or text aliases for the
names) are transmitted within the protocol. For example, in SMTP, the
names of the verbs are part of the command stream. The names of protocol
elements are not normally seen by end users.

name spaces

[[ No definition yet. ]] <NONE>

Many items in Internet protocols use names to identify content. The
field of names for particular item is called its name space. The names
in a name space may be controlled centrally (such as by IANA) or may
have distributed control, such as the names in the DNS.

on-the-wire encoding

The encoding and decoding used before and after transmission is often
called the "on-the-wire" (or sometimes just "wire") format. <NONE>

Characters are identified by codepoints. Before being transmitted in a
protocol, they must first be encoded. Similarly, when characters are
received in a transmission, they have been encoded, and a protocol that
needs to process the individual characters needs to decode them before
processing.

parsed text

Text strings that searched for subparts. <NONE>

In some protocols, free text in text fields might be parsed. For
example, many mail user agents will parse the words in the text of the
Subject: field to attempt to thread based on the "Re:" prefix.

charset identification

Specification of the charset used on a string of text. <NONE>

Protocols that allow more than one charset to be used usually require
that the text be identified with the appropriate charset. Without this
identification, a program looking at the text cannot definitively
discern the charset of the text. Charset identification is also called
"charset tagging".

language identification

Specification of the human language used on a string of text. <NONE>

Some protocols allow text that is meant for machine processing to be
identified with the language used in the text. Such identification is
important for machine-processing of the text, such as by systems that
render the text by speaking it. Language identification is also called
"language tagging".

MIME

MIME (Multipurpose Internet Mail Extensions) is a message format that
allows for textual message bodies and headers in character sets other
than US-ASCII in formats that require ASCII (most notably, RFC 2822, the
standard for Internet mail headers). MIME is described in RFCs 2045
through 2049. <NONE>

transfer encoding syntax

A transfer encoding syntax (TES) (sometimes called a transfer encoding
scheme) is a reversible transform of already-encoded data represented in
one or more character encoding schemes. <NONE>

TESs are useful for encoding types of character data into an another
format, usually for allowing new types of data to be transmitted over
legacy protocols. Examples of TESs used in the IETF include Base64 and
quoted-printable.

Base64

Base64 is a transfer encoding syntax that allows binary data to be
represented by the ASCII characters A through Z, a through z, 0 through
9, +, /, and =. It is defined in RFC 2045. <NONE>

quoted printable

Quoted printable is a transfer encoding syntax that allows strings that
have non-ASCII characters mixed in with mostly ASCII printable
characters to be somewhat human readable. It is described in RFC 2047.
<NONE>

The quoted printable syntax is generally considered to generally be a
failure at being readable. It is jokingly referred to as "quoted
unreadable".

XML

XML (which is an approximate abbreviation for Extensible Markup
Language) is a popular method for structuring text. XML text is
explicitly tagged with charsets. The specification for XML can be found
at <http://www.w3.org/XML/>. <NONE>

ASN.1 text formats

The ASN.1 data description language has many formats for text items. The
formats allow for different repertoires and different encodings. Some of
the formats that appear in IETF standards based on ASN.1 include
IA5String (all ASCII characters), PrintableString (most ASCII
characters, but missing many punctuation characters), BMPString
(characters from ISO/IEC 10646 plane 0 in UTF-16BE format), UTF8String
(just as the name implies), and TeletexString (also called T61String;
the repertoire changes over time).

ASCII-compatible encoding (ACE)

Starting in 1996, many ASCII-compatible encoding schemes (which are
actually transfer encoding syntaxes) have been proposed as possible
solutions for internationalizing host names. Their goal is to be able to
encode any string of ISO/IEC 10646 characters as legal DNS host names
(as described in STD 13). At the time of this writing, no ACE has become
an IETF standard.


7. Other Common Terms In Internationalization

This is a hodge-podge of other terms that have appeared in
internationalization discussions in the IETF. It is likely that
additional terms will be added as this document matures.

locale and region

Because languages differ from country to country (and even region to
region within a country), the locale of the user of internationalized
text can often be an important factor. Typically, the locale information
for a user includes the language(s) used. <NONE>

Locale issues go beyond character use, and can include things such as
the display format for currency, dates, and times. Some locales
(especially the popular "C" and "POSIX" locales) do NOT include language
information.

Latin characters

"Latin characters" is a not-precise term for characters historically
related to ancient Greek script and currently used throughout the world.
The base Latin characters make up the ASCII repertoire and have been
augmented by many single and multiple diacritics and quite a few other
characters. ISO/IEC 10646 encodes the Latin characters in the ranges
U+0020..U+024F, U+1E00..U+1EFF, and other ranges. <NONE>

romanization

The transliteration of a non-Latin script into Latin characters. <NONE>

Because of the widespread use of Latin characters, people have tried to
represent many languages that are not based on a Latin repertoire in
Latin. For example, there are two popular romanizations of Chinese:
Wade-Giles and Pinyin, the latter of which is by far more common today.
Most romanization systems are inexact and do not give perfect round trip
mappings between the native script and the Latin characters.

CJK characters and Han characters

The ideographic characters used in Chinese, Japanese, Korean, and
traditional Vietnamese scripts are often called "CJK characters" after
the initial letters of the script names in English. They are also called
"Han characters", after the romanized translation of the term in Chinese
that is often used for these characters. <NONE>

Note that CJK and Han characters do not include the phonetic characters
of the Japanese or Korean alphabets.

translation

The process of converting one language to another. <NONE>

Most language translation systems are inexact and do not give one-to-one
round trip mappings between the languages.

transliteration

The process of converting one script to another. <NONE>

Most script transliterations are exact, and many have perfect round-trip
mappings.

regular expressions

Regular expressions are a language used to search for text within
strings, and possibly modify the text found with other text. <NONE>

Pattern matching for text involves being able to represent one or more
code points in an abstract notation, such as searching for all capital
Latin letters or all punctuation. The most common mechanism in IETF
protocols for naming such patterns is the use of regular expressions.
There is no single regular expression language, but there are numerous
very similar dialects.

private use

ISO/IEC 10646 code points from U+E000 to U+F8FF, U+F0000 to U+FFFFD, and
U+100000 to U+10FFFD are available for private use. This refers to code
points of the standard whose interpretation is not specified by the
standard and whose use may be determined by private agreement among
cooperating users. <UNICODE>

The use of these "private use" characters is defined by the parties who
transmit and receive them, and is thus not appropriate for
standardization.

8. Security Considerations

Security is not discussed in this document.


9. References

[CHARMOD] Character Model for the World Wide Web 1.0, W3C,
http://www.w3.org/TR/charmod/

[FRAMEWORK] ISO/IEC TR 11017:1997(E). Information technology - Framework
for internationalization, prepared by ISO/IEC JTC 1/SC 22/WG 20.

[IDN-REQ] "Requirements of Internationalized Domain Names", work in
progress (draft-ietf-idn-requirements), Z. Wenzel and J. Seng.

[ISOIEC10646] ISO/IEC 10646-1:2000. International Standard --
Information technology -- Universal Multiple-Octet Coded Character Set
(UCS) -- Part 1: Architecture and Basic Multilingual Plane.

[RFC2277] "IETF Policy on Character Sets and Languages", RFC 2277, H.
Alvestrand.

[RFC2279] "UTF-8, a transformation format of ISO 10646", RFC 2279, F.
Yergeau.

[RFC2781] "UTF-16, an encoding of ISO 10646", RFC 2781, P. Hoffman and
F. Yergeau.

[RFC3066] "Tags for the Identification of Languages", RFC 3066, H.
Alvestrand.

[UNICODE] The Unicode Consortium, "The Unicode Standard -- Version 3.0",
ISBN 0-201-61633-5. Described at
<http://www.unicode.org/unicode/standard/versions/Unicode3.0.html>.

[US-ASCII]  Coded Character Set -- 7-bit American Standard Code for
Information Interchange, ANSI X3.4-1986.

[UTR15] "Unicode Normalization Forms", Unicode Technical Report #15, M.
Davis & M. Duerst.


10. Additional Interesting Reading

ALA-LC Romanization Tables, Randall Barry (ed.), ISBN 0844409405

Blackwell Encyclopedia of Writing Systems, Florian Coulmas, ISBN
063121481X

The World's Writing Systems, Peter Daniels and William Bright, ISBN
0195079930

Writing Systems of the World, Akira Nakanishi, ISBN 0804816549


11. Index

alphabetic -- 4.1
ASCII-compatible encoding (ACE) -- 6
ASN.1 text formats -- 6
Base64 -- 6
Basic Multilingual Plane (BMP) -- 3.2
bidirectional display -- 5
case -- 4
character -- 2
character encoding form -- 2
character encoding scheme -- 2
charset -- 2
charset identification -- 6
CJK characters and Han characters -- 7
code table -- 4
coded character -- 2
coded character set -- 2
combining character -- 4
compatibility character -- 4.1
composite sequence -- 4
control character -- 4.1
diacritic -- 4.1
displaying and rendering text -- 2
font -- 5
formatting character -- 4.1
glyph -- 5
glyph code -- 5
graphic symbol -- 5
i18n, l10n -- 2
ideographic -- 4.1
input methods -- 5
internationalization -- 2
ISO -- 3.1
language -- 2
language identification -- 6
Latin characters -- 7
local and regional standards organizations -- 3.1
locale and region -- 7
localization -- 2
MIME -- 6
multilingual -- 2
name spaces -- 6
nonspacing character -- 4.1
normalization -- 4
on-the-wire encoding -- 6
parsed text -- 6
private use -- 7
protocol elements -- 6
punctuation -- 4.1
quoted printable -- 6
regular expressions -- 7
rendering rules -- 5
romanization -- 7
script -- 2
sorting and collation -- 4
symbol -- 4.1
transcoding -- 2
transfer encoding syntax -- 6
translation -- 7
transliteration -- 7
UCS-2 and UCS-4 -- 3.2
undisplayable character -- 5
Unicode Consortium -- 3.1
UTF-16, UTF-16BE, and UTF-16LE -- 3.2
UTF-8 -- 3.2
World Wide Web Consortium -- 3.1
XML -- 6


A. Acknowledgements

The definitions in this document come from many sources, including a
wide variety of IETF documents.

James Seng contributed to the initial outline of this document. Harald
Alvestrand and Martin Duerst made extensive useful comments on an early
version. Others who contributed to the development include:

Jacob Palme
Susan Harris
Johan van Wingen
Yuri Demchenko
Peter Constable
Zita Wenzel


B. Changes between versions -01 and -02

Radical restructuring. Scrapped many terms that are not used in the IETF
context. Changed definitions to those from ISO and Unicode. Essentially
an almost complete rewrite.


C. Author Contact Information

Paul Hoffman
Internet Mail Consortium and VPN Consortium
127 Segre Place
Santa Cruz, CA  95060 USA
paul.hoffman@imc.org and paul.hoffman@vpnc.org