what is the concept of archiving?

[Linus Arver]

Hello,

I am curious about the following interactive functions --- they all deal
with archiving messages:

	notmuch-tree-archive-thread
	notmuch-show-archive-thread
	notmuch-show-archive-message
	notmuch-tree-archive-message
	notmuch-search-archive-thread
	notmuch-show-advance-and-archive
	notmuch-show-stash-mlarchive-link
	notmuch-show-archive-thread-then-next
	notmuch-show-archive-thread-then-exit
	notmuch-tree-archive-message-then-next
	notmuch-show-stash-mlarchive-link-and-go
	notmuch-show-archive-message-then-next-or-exit
	notmuch-show-archive-message-then-next-or-next-thread

Unfortunately, I cannot find enough information online about what any of
these functions do, or what the concept of "archiving" means. From
reading some of the sources in notmuch-tree.el I found out that
archiving a message results in "applying the tag changes in
`notmuch-archive-tags' to it" but I am not sure what this means.

I found out that the key bindings are in that same file, which assigns
"a" to notmuch-tree-archive-message-then-next; when I press "a" in my
inbox view (all messages tagged "inbox"), it appears to just remove the
"inbox" tag. I have some questions:

(1) What is the point of archiving (what problem does it solve)?

(2) Do any other things happen to such archived messages, apart from the
tag being removed?

(3) How do I un-archive these messages, if I press the "a" key by
accident?

Thanks,
Linus