Sometime users post articles (or series of articles) that have been encoded in some way or other. Gnus can decode them for you.
All these functions use the process/prefix convention (see Process/Prefix) for finding out what articles to work on, with the extension that a “single article” means “a single series”. Gnus can find out by itself what articles belong to a series, decode all the articles and unpack/view/save the resulting file(s).
Gnus guesses what articles are in the series according to the following simplish rule: The subjects must be (nearly) identical, except for the last two numbers of the line. (Spaces are largely ignored, however.)
For example: If you choose a subject called ‘cat.gif (2/3)’, Gnus will find all the articles that match the regexp ‘^cat.gif ([0-9]+/[0-9]+).*$’.
Subjects that are non-standard, like ‘cat.gif (2/3) Part 6 of a series’, will not be properly recognized by any of the automatic viewing commands, and you have to mark the articles manually with #.