Encode::MIME::HeaderSection: Perl Programmers Reference Guide (3)
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NAMEEncode::MIME::Header -- MIME 'B' and 'Q' header encoding
use Encode qw/encode decode/; $utf8 = decode('MIME-Header', $header); $header = encode('MIME-Header', $utf8);
ABSTRACTThis module implements RFC 2047 Mime Header Encoding. There are 3 variant encoding names; "MIME-Header", "MIME-B" and "MIME-Q". The difference is described below
decode() encode() ---------------------------------------------- MIME-Header Both B and Q =?UTF-8?B?....?= MIME-B B only; Q croaks =?UTF-8?B?....?= MIME-Q Q only; B croaks =?UTF-8?Q?....?=
DESCRIPTIONWhen you decode(=?encoding?X?ENCODED WORD?=), ENCODED WORD is extracted and decoded for X encoding (B for Base64, Q for Quoted-Printable). Then the decoded chunk is fed to decode(encoding). So long as encoding is supported by Encode, any source encoding is fine.
When you encode, it just encodes UTF-8 string with X encoding then quoted with =?UTF-8?X?....?= . The parts that RFC 2047 forbids to encode are left as is and long lines are folded within 76 bytes per line.
BUGSIt would be nice to support encoding to non-UTF8, such as =?ISO-2022-JP? and =?ISO-8859-1?= but that makes the implementation too complicated. These days major mail agents all support =?UTF-8? so I think it is just good enough.
RFC 2047, <http://www.faqs.org/rfcs/rfc2047.html> and many other locations.