Editing YEnc (section)

==How yEnc works==
Usenet and email message bodies were intended to contain only ASCII characters ({{IETF RFC|822}} or {{IETF RFC|2822}}).  Most competing encodings represent binary files by converting them into printable ASCII characters, because the range of printable ASCII characters is supported by most operating systems. However, since this reduces the available character set considerably, there is significant overhead (wasted bandwidth) over 8bit-byte networks. For example, in uuencode and Base64, three bytes of data are encoded into four printable ASCII characters, which equals four bytes, a 33% overhead (not including the overhead from headers). yEnc uses one character (one byte) to represent one byte of the file, with a few exceptions.

yEnc assumes that binary data mostly can be transmitted through Usenet and email. Therefore, 252 of the 256 possible bytes are passed through unencoded as a single byte, whether that result is a printable ASCII character or not. Only [[Null character|NUL]], [[line feed|LF]], [[Carriage return|CR]], and = are [[Escape character|escaped]]. LF and CR are escaped because the RFCs that define [[Internet]] messages still require that carriage returns and line feeds have special meaning in a mail message. = is the escape character, so it itself is escaped. NUL is also escaped because of problems handling null characters in common code, although as an optimization yEnc adds 42 to every source byte so that, not uncommon, long stretches of zero bytes do not require a lot of escaping.

There is no [[Request for Comments|RFC]] or other standards document describing yEnc.<ref name="AHD2006">{{cite book |url=https://archive.org/details/highdefinitionan00edit/page/353/mode/2up |title=High Definition: An A to Z Guide to Personal Technology |year=2006 |isbn=978-0618714896 |pages=353 |quote=While there are no official standards for yEnc, it is widely used for posting binary files on newsgroups |url-access=registration}}</ref> The yEnc homepage contains a {{cns|date=February 2019|draft informal}} specification and a grammar {{cns|date=February 2019|(which contradict {{IETF RFC|2822}} and {{IETF RFC|2045}}),}} {{cns|date=February 2019|although neither has been submitted to the [[Internet Engineering Task Force]].}}

{{cns|date=February 2019|As with uuencoding, despite its flaws, yEnc remains{{when|date=February 2019}} active and effective on Usenet.}}  The yEnc homepage states that "''all major newsreaders have been extended to yEnc support''". [[Microsoft]]'s [[Outlook Express]], [[Windows Mail]] and [[Windows Live Mail]] do not provide yEnc support for either news or mail, but there are [[Plug-in (computing)|plug-ins]] available. [[Mozilla Thunderbird]] will decode single-part yEnc files, but is not able to combine multi-part binaries.<ref>{{cite mailing list|url=http://markmail.org/message/uk4w6mth3p7pe5xf|title=Yenc support in Thunderbird?|date=2006-05-18|mailing-list=org.mozilla.lists.support-thunderbird}}
<!--
> Thunderbird will automatically decode yEnc binaries, but cannot combine
> multi-part binaries, which means you can only use it on single-part
> binaries.

Yes, and only those yenc binaries that do not have a part one of one
header entry on the second line of the header.  TB treats that as a
multi-part file even though it is a single part file.
--></ref>