s-o-1036 June 1994

4.5. Non-ASCII Characters In Headers

All  octets found in headers MUST be ASCII characters.  How-
ever, it is desirable to have a way  of  encoding  non-ASCII
characters,  especially  in "human-readable" headers such as
Subject.  MIME [rrr]  provides  a  way  to  do  this.   Full
details  may be found in the MIME specifications; herewith a
quick summary to alert software authors to the issues...

     encoded-word  = "=?" charset "?" encoding "?" codes "?="
     charset       = 1*tag-char
     encoding      = 1*tag-char
     tag-char      = <ASCII printable character except !()<>@,;:\"[]/?=>
     codes         = 1*code-char
     code-char     = <ASCII printable character except ?>

An encoded word is a sequence of ASCII printable  characters
that  specifies the character set, encoding method, and bits
of (potentially) non-ASCII characters.   Encoded  words  are
allowed  only in certain positions in certain headers.  Spe-
cific headers impose restrictions on the content of  encoded
words beyond that specified in this section.  Posting agents
MUST ensure that any material  resembling  an  encoded  word
(complete  with  all delimiters), in a context where encoded
words may appear, really is an encoded word.

     NOTE: The  syntax  is  a  bit  ugly,  but  it  was
     designed  to  minimize  chances  of confusion with
     legitimate header contents, and to satisfy  diffi-
     cult constraints on use within existing headers.

An  encoded word MUST not be more than 75 octets long.  Each
line of a header containing encoded word(s) MUST be at  most