Article buffer coding system for filtered MIME parts

[Giorgos Keramidas]

When I get HTML attachments as MIME parts, and I hit RET twice on the
button of an HTML attachment, Gnus displays all Greek characters as \???
octals in the filtered output, i.e.:

:         character: \335 (4194269, #o17777735, #x3fffdd)
: preferred charset: eight-bit (Raw bytes 0-255)
:        code point: 0xDD
:            syntax: w    which means: word
:       buffer code: #xDD
:         file code: #xDD (encoded by coding system raw-text-unix)
:           display: not encodable for terminal
:
: Character code properties are not shown: customize what to show
:
: There are text properties here:
:   auto-composed        t

This is shown by typing `C-u C-x =' on a character returned by
elinks(1), after an HTML attachment was filtered through:

    elinks -dump -dump-charset iso-8859-7 '%s'

Is there some way to convince Gnus to show the output of the filters
used iso-8859-7 as its coding system?