Network Working Group K. Moore

Request for Comments: 2047 University of Tennessee

Obsoletes: 1521, 1522, 1590 November 1996

Category: Standards Track

MIME (Multipurpose Internet Mail Extensions) Part Three:

Message Header Extensions for Non-ASCII Text

Status of this Memo

This document specifies an Internet standards track protocol for the

Internet community, and requests discussion and suggestions for

improvements. Please refer to the current edition of the "Internet

Official Protocol Standards" (STD 1) for the standardization state

and status of this protocol. Distribution of this memo is unlimited.

Abstract

STD 11, RFC 822, defines a message representation protocol specifying

considerable detail about US-ASCII message headers, and leaves the

message content, or message body, as flat US-ASCII text. This set of

documents, collectively called the Multipurpose Internet Mail

Extensions, or MIME, redefines the format of messages to allow for

(1) textual message bodies in character sets other than US-ASCII,

(2) an extensible set of different formats for non-textual message

bodies,

(3) multi-part message bodies, and

(4) textual header information in character sets other than US-ASCII.

These documents are based on earlier work documented in RFC 934, STD

11, and RFC 1049, but extends and revises them. Because RFC 822 said

so little about message bodies, these documents are largely

orthogonal to (rather than a revision of) RFC 822.

This particular document is the third document in the series. It

describes extensions to RFC 822 to allow non-US-ASCII text data in

Internet mail header fields.

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RFC 2047 Message Header Extensions November 1996

Other documents in this series include:

RFC 2045, which specifies the various headers used to describe

the structure of MIME messages.

RFC 2046, which defines the general structure of the MIME media

typing system and defines an initial set of media types,

RFC 2048, which specifies various IANA registration procedures

for MIME-related facilities, and

RFC 2049, which describes MIME conformance criteria and

provides some illustrative examples of MIME message formats,

acknowledgements, and the bibliography.

These documents are revisions of RFCs 1521, 1522, and 1590, which

themselves were revisions of RFCs 1341 and 1342. An appendix in RFC

2049 describes differences and changes from previous versions.

1. Introduction

RFC 2045 describes a mechanism for denoting textual body parts which

are coded in various character sets, as well as methods for encoding

such body parts as sequences of printable US-ASCII characters. This

memo describes similar techniques to allow the encoding of non-ASCII

text in various portions of a RFC 822 [2] message header, in a manner

which is unlikely to confuse existing message handling software.

Like the encoding techniques described in RFC 2045, the techniques

outlined here were designed to allow the use of non-ASCII characters

in message headers in a way which is unlikely to be disturbed by the

quirks of existing Internet mail handling programs. In particular,

some mail relaying programs are known to (a) delete some message

header fields while retaining others, (b) rearrange the order of

addresses in To or Cc fields, (c) rearrange the (vertical) order of

header fields, and/or (d) "wrap" message headers at different places

than those in the original message. In addition, some mail reading

programs are known to have difficulty correctly parsing message

headers which, while legal according to RFC 822, make use of

backslash-quoting to "hide" special characters such as "<", ",", or

":", or which exploit other infrequently-used features of that

specification.

While it is unfortunate that these programs do not correctly

interpret RFC 822 headers, to "break" these programs would cause

severe operational problems for the Internet mail system. The

extensions described in this memo therefore do not rely on little-

used features of RFC 822.

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RFC 2047 Message Header Extensions November 1996

Instead, certain sequences of "ordinary" printable ASCII characters

(known as "encoded-words") are reserved for use as encoded data. The

syntax of encoded-words is such that they are unlikely to

"accidentally" appear as normal text in message headers.

Furthermore, the characters used in encoded-words are restricted to

those which do not have special meanings in the context in which the

encoded-word appears.

Generally, an "encoded-word" is a sequence of printable ASCII

characters that begins with "=?", ends with "?=", and has two "?"s in

between. It specifies a character set and an encoding method, and

also includes the original text encoded as graphic ASCII characters,

according to the rules for that encoding method.

A mail composer that implements this specification will provide a

means of inputting non-ASCII text in header fields, but will

translate these fields (or appropriate portions of these fields) into

encoded-words before inserting them into the message header.

A mail reader that implements this specification will recognize

encoded-words when they appear in certain portions of the message

header. Instead of displaying the encoded-word "as is", it will

reverse the encoding and display the original text in the designated

character set.

NOTES

This memo relies heavily on notation and terms defined RFC 822 and

RFC 2045. In particular, the syntax for the ABNF used in this memo

is defined in RFC 822, as well as many of the terminal or nonterminal

symbols from RFC 822 are used in the grammar for the header

extensions defined here. Among the symbols defined in RFC 822 and

referenced in this memo are: 'addr-spec', 'atom', 'CHAR', 'comment',

'CTLs', 'ctext', 'linear-white-space', 'phrase', 'quoted-pair'.

'quoted-string', 'SPACE', and 'word'. Successful implementation of

this protocol extension requires careful attention to the RFC 822

definitions of these terms.

When the term "ASCII" appears in this memo, it refers to the "7-Bit

American Standard Code for Information Interchange", ANSI X3.4-1986.

The MIME charset name for this character set is "US-ASCII". When not

specifically referring to the MIME charset name, this document uses

the term "ASCII", both for brevity and for consistency with RFC 822.

However, implementors are warned that the character set name must be

spelled "US-ASCII" in MIME message and body part headers.

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RFC 2047 Message Header Extensions November 1996

This memo specifies a protocol for the representation of non-ASCII

text in message headers. It specifically DOES NOT define any

translation between "8-bit headers" and pure ASCII headers, nor is

any such translation assumed to be possible.

2. Syntax of encoded-words

An 'encoded-word' is defined by the following ABNF grammar. The

notation of RFC 822 is used, with the exception that white space

characters MUST NOT appear between components of an 'encoded-word'.

encoded-word = "=?" charset "?" encoding "?" encoded-text "?="

charset = token ; see section 3

encoding = token ; see section 4

token = 1*<Any CHAR except SPACE, CTLs, and especials>

especials = "(" / ")" / "<" / ">" / "@" / "," / ";" / ":" / "

<"> / "/" / "[" / "]" / "?" / "." / "="

encoded-text = 1*<Any printable ASCII character other than "?"

or SPACE>

; (but see "Use of encoded-words in message

; headers", section 5)

Both 'encoding' and 'charset' names are case-independent. Thus the

charset name "ISO-8859-1" is equivalent to "iso-8859-1", and the

encoding named "Q" may be spelled either "Q" or "q".

An 'encoded-word' may not be more than 75 characters long, including

'charset', 'encoding', 'encoded-text', and delimiters. If it is

desirable to encode more text than will fit in an 'encoded-word' of

75 characters, multiple 'encoded-word's (separated by CRLF SPACE) may

be used.

While there is no limit to the length of a multiple-line header

field, each line of a header field that contains one or more

'encoded-word's is limited to 76 characters.

The length restrictions are included both to ease interoperability

through internetwork mail gateways, and to impose a limit on the

amount of lookahead a header parser must employ (while looking for a

final ?= delimiter) before it can decide whether a token is an

"encoded-word" or something else.

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IMPORTANT: 'encoded-word's are designed to be recognized as 'atom's

by an RFC 822 parser. As a consequence, unencoded white space

characters (such as SPACE and HTAB) are FORBIDDEN within an

'encoded-word'. For example, the character sequence

=?iso-8859-1?q?this is some text?=

would be parsed as four 'atom's, rather than as a single 'atom' (by

an RFC 822 parser) or 'encoded-word' (by a parser which understands

'encoded-words'). The correct way to encode the string "this is some

text" is to encode the SPACE characters as well, e.g.

=?iso-8859-1?q?this=20is=20some=20text?=

The characters which may appear in 'encoded-text' are further

restricted by the rules in section 5.

3. Character sets

The 'charset' portion of an 'encoded-word' specifies the character

set associated with the unencoded text. A 'charset' can be any of

the character set names allowed in an MIME "charset" parameter of a

"text/plain" body part, or any character set name registered with

IANA for use with the MIME text/plain content-type.

Some character sets use code-switching techniques to switch between

"ASCII mode" and other modes. If unencoded text in an 'encoded-word'

contains a sequence which causes the charset interpreter to switch

out of ASCII mode, it MUST contain additional control codes such that

ASCII mode is again selected at the end of the 'encoded-word'. (This

rule applies separately to each 'encoded-word', including adjacent

'encoded-word's within a single header field.)

When there is a possibility of using more than one character set to

represent the text in an 'encoded-word', and in the absence of

private agreements between sender and recipients of a message, it is

recommended that members of the ISO-8859-* series be used in

preference to other character sets.

4. Encodings

Initially, the legal values for "encoding" are "Q" and "B". These

encodings are described below. The "Q" encoding is recommended for

use when most of the characters to be encoded are in the ASCII

character set; otherwise, the "B" encoding should be used.

Nevertheless, a mail reader which claims to recognize 'encoded-word's

MUST be able to accept either encoding for any character set which it

supports.

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Only a subset of the printable ASCII characters may be used in

'encoded-text'. Space and tab characters are not allowed, so that

the beginning and end of an 'encoded-word' are obvious. The "?"

character is used within an 'encoded-word' to separate the various

portions of the 'encoded-word' from one another, and thus cannot

appear in the 'encoded-text' portion. Other characters are also

illegal in certain contexts. For example, an 'encoded-word' in a

'phrase' preceding an address in a From header field may not contain

any of the "specials" defined in RFC 822. Finally, certain other

characters are disallowed in some contexts, to ensure reliability for

messages that pass through internetwork mail gateways.

The "B" encoding automatically meets these requirements. The "Q"

encoding allows a wide range of printable characters to be used in

non-critical locations in the message header (e.g., Subject), with

fewer characters available for use in other locations.

4.1. The "B" encoding

The "B" encoding is identical to the "BASE64" encoding defined by RFC

2045.

4.2. The "Q" encoding

The "Q" encoding is similar to the "Quoted-Printable" content-

transfer-encoding defined in RFC 2045. It is designed to allow text

containing mostly ASCII characters to be decipherable on an ASCII

terminal without decoding.

(1) Any 8-bit value may be represented by a "=" followed by two

hexadecimal digits. For example, if the character set in use

were ISO-8859-1, the "=" character would thus be encoded as

"=3D", and a SPACE by "=20". (Upper case should be used for

hexadecimal digits "A" through "F".)

(2) The 8-bit hexadecimal value 20 (e.g., ISO-8859-1 SPACE) may be

represented as "_" (underscore, ASCII 95.). (This character may

not pass through some internetwork mail gateways, but its use

will greatly enhance readability of "Q" encoded data with mail

readers that do not support this encoding.) Note that the "_"

always represents hexadecimal 20, even if the SPACE character

occupies a different code position in the character set in use.

(3) 8-bit values which correspond to printable ASCII characters other

than "=", "?", and "_" (underscore), MAY be represented as those

characters. (But see section 5 for restrictions.) In

particular, SPACE and TAB MUST NOT be represented as themselves

within encoded words.

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5. Use of encoded-words in message headers

An 'encoded-word' may appear in a message header or body part header

according to the following rules:

(1) An 'encoded-word' may replace a 'text' token (as defined by RFC 822)

in any Subject or Comments header field, any extension message

header field, or any MIME body part field for which the field body

is defined as '*text'. An 'encoded-word' may also appear in any

user-defined ("X-") message or body part header field.

Ordinary ASCII text and 'encoded-word's may appear together in the

same header field. However, an 'encoded-word' that appears in a

header field defined as '*text' MUST be separated from any adjacent

'encoded-word' or 'text' by 'linear-white-space'.

(2) An 'encoded-word' may appear within a 'comment' delimited by "(" and

")", i.e., wherever a 'ctext' is allowed. More precisely, the RFC

822 ABNF definition for 'comment' is amended as follows:

comment = "(" *(ctext / quoted-pair / comment / encoded-word) ")"

A "Q"-encoded 'encoded-word' which appears in a 'comment' MUST NOT

contain the characters "(", ")" or "

'encoded-word' that appears in a 'comment' MUST be separated from

any adjacent 'encoded-word' or 'ctext' by 'linear-white-space'.

It is important to note that 'comment's are only recognized inside

"structured" field bodies. In fields whose bodies are defined as

'*text', "(" and ")" are treated as ordinary characters rather than

comment delimiters, and rule (1) of this section applies. (See RFC

822, sections 3.1.2 and 3.1.3)

(3) As a replacement for a 'word' entity within a 'phrase', for example,

one that precedes an address in a From, To, or Cc header. The ABNF

definition for 'phrase' from RFC 822 thus becomes:

phrase = 1*( encoded-word / word )

In this case the set of characters that may be used in a "Q"-encoded

'encoded-word' is restricted to: <upper and lower case ASCII

letters, decimal digits, "!", "*", " ", "-", "/", "=", and "_"

(underscore, ASCII 95.)>. An 'encoded-word' that appears within a

'phrase' MUST be separated from any adjacent 'word', 'text' or

'special' by 'linear-white-space'.

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These are the ONLY locations where an 'encoded-word' may appear. In

particular:

An 'encoded-word' MUST NOT appear in any portion of an 'addr-spec'.

An 'encoded-word' MUST NOT appear within a 'quoted-string'.

An 'encoded-word' MUST NOT be used in a Received header field.

An 'encoded-word' MUST NOT be used in parameter of a MIME

Content-Type or Content-Disposition field, or in any structured

field body except within a 'comment' or 'phrase'.

The 'encoded-text' in an 'encoded-word' must be self-contained;

'encoded-text' MUST NOT be continued from one 'encoded-word' to

another. This implies that the 'encoded-text' portion of a "B"

'encoded-word' will be a multiple of 4 characters long; for a "Q"

'encoded-word', any "=" character that appears in the 'encoded-text'

portion will be followed by two hexadecimal characters.

Each 'encoded-word' MUST encode an integral number of octets. The

'encoded-text' in each 'encoded-word' must be well-formed according

to the encoding specified; the 'encoded-text' may not be continued in

the next 'encoded-word'. (For example, "=?charset?Q?=?=

=?charset?Q?AB?=" would be illegal, because the two hex digits "AB"

must follow the "=" in the same 'encoded-word'.)

Each 'encoded-word' MUST represent an integral number of characters.

A multi-octet character may not be split across adjacent 'encoded-

word's.

Only printable and white space character data should be encoded using

this scheme. However, since these encoding schemes allow the

encoding of arbitrary octet values, mail readers that implement this

decoding should also ensure that display of the decoded data on the

recipient's terminal will not cause unwanted side-effects.

Use of these methods to encode non-textual data (e.g., pictures or

sounds) is not defined by this memo. Use of 'encoded-word's to

represent strings of purely ASCII characters is allowed, but

discouraged. In rare cases it may be necessary to encode ordinary

text that looks like an 'encoded-word'.

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6. Support of 'encoded-word's by mail readers

6.1. Recognition of 'encoded-word's in message headers

A mail reader must parse the message and body part headers according

to the rules in RFC 822 to correctly recognize 'encoded-word's.

'encoded-word's are to be recognized as follows:

(1) Any message or body part header field defined as '*text', or any

user-defined header field, should be parsed as follows: Beginning

at the start of the field-body and immediately following each

occurrence of 'linear-white-space', each sequence of up to 75

printable characters (not containing any 'linear-white-space')

should be examined to see if it is an 'encoded-word' according to

the syntax rules in section 2. Any other sequence of printable

characters should be treated as ordinary ASCII text.

(2) Any header field not defined as '*text' should be parsed

according to the syntax rules for that header field. However,

any 'word' that appears within a 'phrase' should be treated as an

'encoded-word' if it meets the syntax rules in section 2.

Otherwise it should be treated as an ordinary 'word'.

(3) Within a 'comment', any sequence of up to 75 printable characters

(not containing 'linear-white-space'), that meets the syntax

rules in section 2, should be treated as an 'encoded-word'.

Otherwise it should be treated as normal comment text.

(4) A MIME-Version header field is NOT required to be present for

'encoded-word's to be interpreted according to this

specification. One reason for this is that the mail reader is

not expected to parse the entire message header before displaying

lines that may contain 'encoded-word's.

6.2. Display of 'encoded-word's

Any 'encoded-word's so recognized are decoded, and if possible, the

resulting unencoded text is displayed in the original character set.

NOTE: Decoding and display of encoded-words occurs *after* a

structured field body is parsed into tokens. It is therefore

possible to hide 'special' characters in encoded-words which, when

displayed, will be indistinguishable from 'special' characters in the

surrounding text. For this and other reasons, it is NOT generally

possible to translate a message header containing 'encoded-word's to

an unencoded form which can be parsed by an RFC 822 mail reader.

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When displaying a particular header field that contains multiple

'encoded-word's, any 'linear-white-space' that separates a pair of

adjacent 'encoded-word's is ignored. (This is to allow the use of

multiple 'encoded-word's to represent long strings of unencoded text,

without having to separate 'encoded-word's where spaces occur in the

unencoded text.)

In the event other encodings are defined in the future, and the mail

reader does not support the encoding used, it may either (a) display

the 'encoded-word' as ordinary text, or (b) substitute an appropriate

message indicating that the text could not be decoded.

If the mail reader does not support the character set used, it may

(a) display the 'encoded-word' as ordinary text (i.e., as it appears

in the header), (b) make a "best effort" to display using such

characters as are available, or (c) substitute an appropriate message

indicating that the decoded text could not be displayed.

If the character set being used employs code-switching techniques,

display of the encoded text implicitly begins in "ASCII mode". In

addition, the mail reader must ensure that the output device is once

again in "ASCII mode" after the 'encoded-word' is displayed.

6.3. Mail reader handling of incorrectly formed 'encoded-word's

It is possible that an 'encoded-word' that is legal according to the

syntax defined in section 2, is incorrectly formed according to the

rules for the encoding being used. For example:

(1) An 'encoded-word' which contains characters which are not legal

for a particular encoding (for example, a "-" in the "B"

encoding, or a SPACE or HTAB in either the "B" or "Q" encoding),

is incorrectly formed.

(2) Any 'encoded-word' which encodes a non-integral number of

characters or octets is incorrectly formed.

A mail reader need not attempt to display the text associated with an

'encoded-word' that is incorrectly formed. However, a mail reader

MUST NOT prevent the display or handling of a message because an

'encoded-word' is incorrectly formed.

7. Conformance

A mail composing program claiming compliance with this specification

MUST ensure that any string of non-white-space printable ASCII

characters within a '*text' or '*ctext' that begins with "=?" and

ends with "?=" be a valid 'encoded-word'. ("begins" means: at the

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start of the field-body, immediately following 'linear-white-space',

or immediately following a "(" for an 'encoded-word' within '*ctext';

"ends" means: at the end of the field-body, immediately preceding

'linear-white-space', or immediately preceding a ")" for an

'encoded-word' within '*ctext'.) In addition, any 'word' within a

'phrase' that begins with "=?" and ends with "?=" must be a valid

'encoded-word'.

A mail reading program claiming compliance with this specification

must be able to distinguish 'encoded-word's from 'text', 'ctext', or

'word's, according to the rules in section 6, anytime they appear in

appropriate places in message headers. It must support both the "B"

and "Q" encodings for any character set which it supports. The

program must be able to display the unencoded text if the character

set is "US-ASCII". For the ISO-8859-* character sets, the mail

reading program must at least be able to display the characters which

are also in the ASCII set.

8. Examples

The following are examples of message headers containing 'encoded-

word's:

From: =?US-ASCII?Q?Keith_Moore?= <[email protected]>

To: =?ISO-8859-1?Q?Keld_J=F8rn_Simonsen?= <[email protected]>

CC: =?ISO-8859-1?Q?Andr=E9?= Pirard <[email protected]>

Subject: =?ISO-8859-1?B?SWYgeW91IGNhbiByZWFkIHRoaXMgeW8=?=

=?ISO-8859-2?B?dSB1bmRlcnN0YW5kIHRoZSBleGFtcGxlLg==?=

Note: In the first 'encoded-word' of the Subject field above, the

last "=" at the end of the 'encoded-text' is necessary because each

'encoded-word' must be self-contained (the "=" character completes a

group of 4 base64 characters representing 2 octets). An additional

octet could have been encoded in the first 'encoded-word' (so that

the encoded-word would contain an exact multiple of 3 encoded

octets), except that the second 'encoded-word' uses a different

'charset' than the first one.

From: =?ISO-8859-1?Q?Olle_J=E4rnefors?= <[email protected]>

To: [email protected], [email protected]

Subject: Time for ISO 10646?

To: Dave Crocker <[email protected]>

Cc: [email protected], [email protected]

From: =?ISO-8859-1?Q?Patrik_F=E4ltstr=F6m?= <[email protected]>

Subject: Re: RFC-HDR care and feeding

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RFC 2047 Message Header Extensions November 1996

From: Nathaniel Borenstein <[email protected]>

(=?iso-8859-8?b?7eXs SDv4SDp7Oj08A==?=)

To: Greg Vaudreuil <[email protected]>, Ned Freed

<[email protected]>, Keith Moore <[email protected]>

Subject: Test of new header generator

MIME-Version: 1.0

Content-type: text/plain; charset=ISO-8859-1

The following examples illustrate how text containing 'encoded-word's

which appear in a structured field body. The rules are slightly

different for fields defined as '*text' because "(" and ")" are not

recognized as 'comment' delimiters. [Section 5, paragraph (1)].

In each of the following examples, if the same sequence were to occur

in a '*text' field, the "displayed as" form would NOT be treated as

encoded words, but be identical to the "encoded form". This is

because each of the encoded-words in the following examples is

adjacent to a "(" or ")" character.

encoded form displayed as

---------------------------------------------------------------------

(=?ISO-8859-1?Q?a?=) (a)

(=?ISO-8859-1?Q?a?= b) (a b)

Within a 'comment', white space MUST appear between an

'encoded-word' and surrounding text. [Section 5,

paragraph (2)]. However, white space is not needed between

the initial "(" that begins the 'comment', and the

'encoded-word'.

(=?ISO-8859-1?Q?a?= =?ISO-8859-1?Q?b?=) (ab)

White space between adjacent 'encoded-word's is not

displayed.

(=?ISO-8859-1?Q?a?= =?ISO-8859-1?Q?b?=) (ab)

Even multiple SPACEs between 'encoded-word's are ignored

for the purpose of display.

(=?ISO-8859-1?Q?a?= (ab)

=?ISO-8859-1?Q?b?=)

Any amount of linear-space-white between 'encoded-word's,

even if it includes a CRLF followed by one or more SPACEs,

is ignored for the purposes of display.

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(=?ISO-8859-1?Q?a_b?=) (a b)

In order to cause a SPACE to be displayed within a portion

of encoded text, the SPACE MUST be encoded as part of the

'encoded-word'.

(=?ISO-8859-1?Q?a?= =?ISO-8859-2?Q?_b?=) (a b)

In order to cause a SPACE to be displayed between two strings

of encoded text, the SPACE MAY be encoded as part of one of

the 'encoded-word's.

9. References

[RFC 822] Crocker, D., "Standard for the Format of ARPA Internet Text

Messages", STD 11, RFC 822, UDEL, August 1982.

[RFC 2049] Borenstein, N., and N. Freed, "Multipurpose Internet Mail

Extensions (MIME) Part Five: Conformance Criteria and Examples",

RFC 2049, November 1996.

[RFC 2045] Borenstein, N., and N. Freed, "Multipurpose Internet Mail

Extensions (MIME) Part One: Format of Internet Message Bodies",

RFC 2045, November 1996.

[RFC 2046] Borenstein N., and N. Freed, "Multipurpose Internet Mail

Extensions (MIME) Part Two: Media Types", RFC 2046,

November 1996.

[RFC 2048] Freed, N., Klensin, J., and J. Postel, "Multipurpose

Internet Mail Extensions (MIME) Part Four: Registration

Procedures", RFC 2048, November 1996.

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10. Security Considerations

Security issues are not discussed in this memo.

11. Acknowledgements

The author wishes to thank Nathaniel Borenstein, Issac Chan, Lutz

Donnerhacke, Paul Eggert, Ned Freed, Andreas M. Kirchwitz, Olle

Jarnefors, Mike Rosin, Yutaka Sato, Bart Schaefer, and Kazuhiko

Yamamoto, for their helpful advice, insightful comments, and

illuminating questions in response to earlier versions of this

specification.

12. Author's Address

Keith Moore

University of Tennessee

107 Ayres Hall

Knoxville TN 37996-1301

EMail: [email protected]

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Appendix - changes since RFC 1522 (in no particular order)

explicitly state that the MIME-Version is not requried to use

'encoded-word's.

add explicit note that SPACEs and TABs are not allowed within

'encoded-word's, explaining that an 'encoded-word' must look like an

'atom' to an RFC822 parser.values, to be precise).

add examples from Olle Jarnefors (thanks!) which illustrate how

encoded-words with adjacent linear-white-space are displayed.

explicitly list terms defined in RFC822 and referenced in this memo

fix transcription typos that caused one or two lines and a couple of

characters to disappear in the resulting text, due to nroff quirks.

clarify that encoded-words are allowed in '*text' fields in both

RFC822 headers and MIME body part headers, but NOT as parameter

values.

clarify the requirement to switch back to ASCII within the encoded

portion of an 'encoded-word', for any charset that uses code switching

sequences.

add a note about 'encoded-word's being delimited by "(" and ")"

within a comment, but not in a *text (how bizarre!).

fix the Andre Pirard example to get rid of the trailing "_" after

the =E9. (no longer needed post-1342).

clarification: an 'encoded-word' may appear immediately following

the initial "(" or immediately before the final ")" that delimits a

comment, not just adjacent to "(" and ")" *within* *ctext.

add a note to explain that a "B" 'encoded-word' will always have a

multiple of 4 characters in the 'encoded-text' portion.

add note about the "=" in the examples

note that processing of 'encoded-word's occurs *after* parsing, and

some of the implications thereof.

explicitly state that you can't expect to translate between

1522 and either vanilla 822 or so-called "8-bit headers".

explicitly state that 'encoded-word's are not valid within a

'quoted-string'.

Moore Standards Track [Page 15]