Moving feeds/items between channels

Is there a mechanism for moving a feed and/or its items between channels, ideally preserving their items' read/unread states?

What about having a feed's items going into different channels based on various rules (e.g. `` tags in Atom)?

One possible use case is on e.g. my website, I have different categories which serve different purposes, and would benefit from different UX for each one, and it would be nice to have some sort of mechanism to not have to subscribe to each site section under a different channel.

Some of this functionality would be better-expressed by the clients/endpoints rather than Microsub itself but it's not clear where the line should be drawn or how to provide a good UX for it.

Perhaps this could be a case for having a post-update hook where an external filter can take action on an item as it comes in before it is presented to the reader.

Start by reading the existing Microsub specification and the discussion on channel, feed, and item handling. Clarify whether moving items, rule-based routing, and post-update filtering belong in Microsub or in clients/endpoints. Done means a decided scope and a specified mechanism that preserves read/unread state where required.

Written by the indexing model from the issue text.