Module thread 

Message threading after JWZ’s algorithm (https://www.jwz.org/doc/threading.html): containers per message-id, reference chains linked parent→child with loop protection, empty containers pruned by promoting their children. Threads and siblings are ordered by date. JWZ step 5, grouping what is left by subject, is mutt’s pseudo_threads here: see SubjectFallback.

Structs

SubjectFallback

mutt’s subject fallback, which runs unless $strict_threads: a thread root whose subject repeats one already in the mailbox hangs under the message carrying it. It is what keeps mail that arrives with no References at all (a notification robot, a list that strips the headers) reading as one thread.

ThreadOrder

Like thread, ordering threads by their newest message when newest (mutt’s sort_aux = last-date-sent). How the threads themselves are ordered, from mutt’s $sort_aux: by the root’s date or by the newest message under it, oldest first or newest first.

ThreadedItem

One index entry in thread order.

Functions

thread

thread_by

thread_with

Threading proper: reference chains, and then, with a SubjectFallback, what mutt does for the messages whose senders left no chain behind.