=head1 TERMS
+=over 8
+
=item IMAP UID, NNTP article number, on-disk Xapian docid
A sequentially-assigned positive integer. These integers are per-inbox,
part of the PSGI code and not need a separate daemon like
L<public-inbox-nntpd(1)> or L<public-inbox-imapd(1)>
+=item epoch
+
+A git repository used for blob storage. See
+L<public-inbox-v2-format(5)/GIT EPOCHS>.
+
=item keywords, (IMAP|Maildir) flags, mbox Status + X-Status
Private, per-message keywords or flags as described in RFC 8621
section 10.4. These are conveyed in the C<Status:> and
-C<X-Status:> headers for L<mbox(5)>, as IMAP FLAGS (RFC 3501 section 2.3.2),
-or Maildir info flags.
+C<X-Status:> headers for L<mbox(5)>, as system IMAP FLAGS
+(RFC 3501 section 2.3.2), or Maildir info flags.
L<public-inbox-watch(1)> ignores drafts and trashed (deleted)
messages. L<lei-import(1)> ignores trashed (deleted) messages,
ease-of-filtering. This is NOT tied to public-inbox names, as
messages stored by lei may not be public.
+These are similar in spirit to arbitrary freeform "tags"
+in mail software such as L<notmuch(1)> and non-system IMAP FLAGS.
+
+=item volatile metadata (VMD)
+
+For L<lei(1)> users only, this refers to the combination of
+keywords and labels which are subject to frequent change
+independently of immutable message content.
+
+=item IMAP INTERNALDATE, JMAP receivedAt, rt: search prefix
+
+The first valid timestamp value of Received: headers (top first).
+If no Received: header exists, the Date: header is used, and the
+current time if neither header(s) exist. When mirroring via
+git, this is the git commit time.
+
+=item IMAP SENT*, JMAP sentAt, dt: and d: search prefixes
+
+The first valid timestamp value of the Date: header(s).
+If no Date: header exists, the time from the Received: header is
+used, and then the current time if neither header exists.
+When mirroring via git, this is the git author time.
+
+=back
+
=head1 COPYRIGHT
Copyright 2021 all contributors L<mailto:meta@public-inbox.org>