usefor-article-06 November 2001

4.4.1.  Character Sets within Article Headers

   Within article headers, characters are represented as octets
   according to the UTF-8 encoding scheme [RFC 2279] or [ISO/IEC 10646],
   and hence all the characters in Unicode [UNICODE 3.1] or in the
   Universal Multiple-Octet Coded Character Set (UCS) [ISO/IEC 10646]
   (which is essentially a superset of Unicode and expected to remain
   so) are potentially available. However, processing all octets in the
   same manner as US-ASCII characters should ensure correct behaviour in
   most situations.
        NOTE: UTF-8 is an encoding for 16bit (and even 32bit) character
        sets with the property that any octet less than 128 immediately
        represents the corresponding US-ASCII character, thus ensuring
        upwards compatibility with previous practice.  Non-ASCII
        characters from Unicode are represented by sequences of octets
        satisfying the syntax of a UTF8-xtra-char (2.4), which excludes
        certain octet sequences not explicitly permitted by [RFC 2279].
        Unicode includes all characters from the ISO-8859 series of
        characters sets [ISO 8859] (which includes all Cyrillic, Greek
        and Arabic characters) together with the more elaborate
        characters used in Asian countries. See the following section
        for the appropriate treatment of Unicode characters by reading
        agents.

   Notwithstanding the great flexibility permitted by UTF-8, there is
   need for restraint in its use in order that the essential components
   of headers may be discerned using reading agents that cannot present
   the full Unicode range. In particular, header-names and tokens MUST
   be in US-ASCII, and certain other components of headers, as defined
   elsewhere in this standard - notably msg-ids, date-times, dot-atoms,
   domains and path-identities - MUST be in US-ASCII.  Comments, phrases
   (as in addresses) and unstructureds (as in Subject headers) MAY use
   the full range of UTF-8 characters, but SHOULD nevertheless be
   invariant under Unicode normalization NFC [UNICODE 3.1].

        NOTE: Unicode allows for composite characters made up of a
        starter character - which can be a letter, number, punctuation
        mark, or symbol - plus zero or more combining marks (such as
        accents, diacritics, and similar). The requirement that a
        composite be invariant under normalization NFC means that, where
        it could be written in more than one way, only one particular
        one is allowed (for example, the single character E-acute is
        preferred over E followed by a non-spacing acute accent, and A-
        ring is preferred over the Angstrom symbol). At least for the
        main European languages, for which all the needed composites are
        already available as single characters, it is unlikely that
        posting agents will need to take any special steps to ensure
        normalization.

   In the particular case of newsgroup-names (see 5.5) there are more
   stringent requirements regarding the use of UTF-8 and Unicode.

   Where the use of non-ASCII characters, encoded in UTF-8, is permitted
   as above, they MAY also be encoded using the MIME mechanism defined
   in [RFC 2047], but this usage is deprecated within news articles
   (even though it is required in mail messages) since it is less
   legible in older reading agents which support neither it nor UTF-8.
   Nevertheless, reading agents SHOULD support this usage, but only in
   those contexts explicitly mentioned in [RFC 2047].

--- ../usefor-article-05/Character_Sets_within_Article_Headers.out          July 2001
+++ ../usefor-article-06/Character_Sets_within_Article_Headers.out          November 2001
@@ -33,16 +33,18 @@
    the full range of UTF-8 characters, but SHOULD nevertheless be
    invariant under Unicode normalization NFC [UNICODE 3.1].
 
-        NOTE: The effect of normalization NFC is to place composite
-        characters (made by overlaying one character with another) into
-        a canonical form (usually represented by a single character
-        where one is available - thus E-acute is preferred over E
-        followed by a non-spacing acute accent), and to make a
-        consistent choice among equivalent forms (e.g. the Angstrom sign
-        is replaced by A-ring). At least for the main European
-        languages, for which all the needed composites are already
-        available as single characters, it is unlikely that posting
-        agents will need to take any special steps to ensure
+        NOTE: Unicode allows for composite characters made up of a
+        starter character - which can be a letter, number, punctuation
+        mark, or symbol - plus zero or more combining marks (such as
+        accents, diacritics, and similar). The requirement that a
+        composite be invariant under normalization NFC means that, where
+        it could be written in more than one way, only one particular
+        one is allowed (for example, the single character E-acute is
+        preferred over E followed by a non-spacing acute accent, and A-
+        ring is preferred over the Angstrom symbol). At least for the
+        main European languages, for which all the needed composites are
+        already available as single characters, it is unlikely that
+        posting agents will need to take any special steps to ensure
         normalization.
 
    In the particular case of newsgroup-names (see 5.5) there are more