3.9 Threading
Gnus threads articles by
default. To thread is to put responses to articles
directly after the articles they respond to—in a
hierarchical fashion.
Threading is done by looking at the References
headers of the articles. In a perfect world, this would be enough
to build pretty trees, but unfortunately, the
References header is often broken or simply missing.
Weird news propagation exacerbates the problem, so one has to
employ other heuristics to get pleasing results. A plethora of
approaches exists, as detailed in horrible detail in Customizing
Threading.
First, a quick overview of the concepts:
- root
- The top-most article in a thread; the first article in the
thread.
- thread
- A tree-like article structure.
- sub-thread
- A small(er) section of this tree-like structure.
- loose threads
- Threads often lose their roots due to article expiry, or
due to the root already having been read in a previous session,
and not displayed in the summary buffer. We then typically have
many sub-threads that really belong to one thread, but are
without connecting roots. These are called loose
threads.
- thread gathering
- An attempt to gather loose threads into bigger
threads.
- sparse threads
- A thread where the missing articles have been
“guessed” at, and are displayed as empty lines in
the summary buffer.