nil, Gnus will gather all loose subtrees into one big tree
and create a dummy root at the top. (Wait a minute. Root at the top?
Yup.) Loose subtrees occur when the real root has expired, or you’ve
read or killed the root in a previous session.
When there is no real root of a thread, Gnus will have to fudge something. This variable says what fudging method Gnus should use. There are four possible values:
Gnus will make the first of the orphaned articles the parent. This parent will adopt all the other articles. The adopted articles will be marked as such by pointy brackets (‘<>’) instead of the standard square brackets (‘’). This is the default method.
Gnus will create a dummy summary line that will pretend to be the
parent. This dummy line does not correspond to any real article, so
selecting it will just select the first real article after the dummy
gnus-summary-dummy-line-format is used to specify the
format of the dummy roots. It accepts only one format spec: ‘S’,
which is the subject of the article. See Formatting Variables.
If you want all threads to have a dummy root, even the non-gathered
Gnus won’t actually make any article the parent, but simply leave the
subject field of all orphans except the first empty. (Actually, it will
gnus-summary-same-subject as the subject (see Summary Buffer Format).)
Don’t make any article parent at all. Just gather the threads and display them after one another.
Don’t gather loose threads.
Loose threads are gathered by comparing subjects of articles. If this
nil, Gnus requires an exact match between the
subjects of the loose threads before gathering them into one big
super-thread. This might be too strict a requirement, what with the
presence of stupid newsreaders that chop off long subject lines. If
you think so, set this variable to, say, 20 to require that only the
first 20 characters of the subjects have to match. If you set this
variable to a really low number, you’ll find that Gnus will gather
everything in sight into one thread, which isn’t very helpful.
If you set this variable to the special value
fuzzy, Gnus will
use a fuzzy string comparison algorithm on the subjects (see Fuzzy Matching).
This can either be a regular expression or list of regular expressions that match strings that will be removed from subjects if fuzzy subject simplification is used.
If you set
gnus-summary-gather-subject-limit to something as low
as 10, you might consider setting this variable to something sensible:
(setq gnus-simplify-ignored-prefixes (concat "\\`\\[?\\(" (regexp-opt '("looking" "wanted" "followup" "summary" "summary of" "help" "query" "problem" "question" "answer" "reference" "announce" "How can I" "How to" "Comparison of" ;; ... )) "\\)\\s *\\(" (regexp-opt '("for" "for reference" "with" "about")) "\\)?\\]?:?[ \t]*"))
All words that match this regexp will be removed before comparing two subjects.
nil, this variable overrides
gnus-summary-gather-subject-limit. This variable should be a
list of functions to apply to the
Subject string iteratively to
arrive at the simplified version of the string.
Useful functions to put in this list include:
Strip the leading ‘Re:’.
Remove excessive whitespace.
Remove all whitespace.
You may also write your own functions, of course.
Since loose thread gathering is done on subjects only, that might lead
to many false hits, especially with certain common subjects like
‘’ and ‘(none)’. To make the situation slightly better,
you can use the regexp
gnus-summary-gather-exclude-subject to say
what subjects should be excluded from the gathering process.
The default is ‘^ *$\\|^(none)$’.
Gnus gathers threads by looking at
Subject headers. This means
that totally unrelated articles may end up in the same “thread”, which
is confusing. An alternate approach is to look at all the
Message-IDs in all the
References headers to find matches.
This will ensure that no gathered threads ever include unrelated
articles, but it also means that people who have posted with broken
newsreaders won’t be gathered properly. The choice is yours—plague or
This function is the default gathering function and looks at
This function looks at
References headers exclusively.
If you want to test gathering by
References, you could say
(setq gnus-summary-thread-gathering-function 'gnus-gather-threads-by-references)