mutt’s ignore/unignore/hdr_order: which headers the pager’s brief
view shows, and in what order. Entries are lowercase name
prefixes; * matches everything; unignore wins over ignore.
mutt’s list-action menu, in its order: the RFC 2369 List-* headers
a message may carry, each with the URL mutt would act on. mutt
takes the first <mailto:...> in the header and nothing else;
here a header holding only other schemes keeps its first URL, so
the answer can be “only mailto: is supported” rather than “none”.
Header text on its way to a one-line slot in the display. A tab
or a stray control character would be written to the terminal as
it stands: a tab jumps to the next tab stop, pushing the rest of
an index row past the window edge and wrapping it onto a second
line. Mail carries them often enough (a header the sender folded
by hand, an RFC 2047 word that decoded to one), so every such
field passes through here.
Render a MIME entity that is not a file of its own — the plaintext
gpg hands back for a PGP/MIME message — exactly as the pager
renders a message body: the whole tree, attachments announced,
filters applied. Text that is not MIME at all comes back as it is.
The brief header view under rules: weeded (ignore minus
unignore), then sorted by hdr_order position; unlisted names
keep message order after the listed ones.
The message with one header replaced: every existing line for
name (folded continuations included) is dropped, and, when
value is Some and non-empty, one name: value line is written
at the end of the header block. Used by edit-label; the line
ending of the original is kept.
The message with its threading headers replaced: In-Reply-To and
References (folded continuation lines included) are dropped, and
the given ones written at the end of the header block, when there
are any. This is what break-thread and link-threads write back;
mutt does the same to the message itself (mutt_break_thread
clears both, link_threads sets In-Reply-To to the parent’s id).
The line ending of the original is kept.