[8] 内容符号化 bzip / bzip2 / x-bzip / x-bzip2 は HTTP RFC では規定されていませんが、 使用されていることがあるみたいです。 (いずれも同義みたいです。)

[1] 173044 – Support for bzip2 transfer encoding, a la w3m ( 版) https://bugzilla.mozilla.org/show_bug.cgi?id=173044

[2] HTTP compression - Wikipedia, the free encyclopedia ( 版) https://en.wikipedia.org/wiki/HTTP_compression#Content-coding_tokens

bzip2 – compression based on the free bzip2 format, supported by lighttpd[7]

[3] rockdaboot/mget ( 版) https://github.com/rockdaboot/mget

Support for bzip2 Content-Encoding / Accept-Encoding compression type

[4] Feature configuration file (features.conf) ( 版) http://elinks.or.cz/documentation/html/manual.html-chunked/ch01s07.html#CONFIG-BZIP2

Bzip2 Decompression (CONFIG_BZIP2)

This makes ELinks decompress local *.bz2 files. Also, ELinks sends "Accept-Encoding: bzip2" in HTTP requests and decompresses any documents received in that format, but this encoding has not been registered at http://www.iana.org/assignments/http-parameters, so most servers probably won't use it.

Default: enabled if the library is installed

[5] HTTP::Message - search.cpan.org () http://search.cpan.org/~oalders/HTTP-Message-6.13/lib/HTTP/Message.pm

[6] >>5 Content-Encoding として bzip2, x-bzip2 に対応。