German WP users seem to be quite happy with this feature.**Background**
#expiring-watchlist-items brought the ability to temporarily watch pages and files, instead of only having the option to watch indefinitely.
Repeatedly since that feature was deployed in 2020, Howeverusers have asked for the ability to set //default// watchlist expiries, three suggestions came upin particular for watching in general (via watch star) and when performing [[ https://www.mediawiki.org/wiki/Manual:Rollback | rollback ]].
**Acceptance criteria**
* Special:Preferences (under "Watchlist") should have a "Default time period" dropdown for:
# Provide a //Special:Preferences// field for a particular default span. Rather than ##infinit## it might be wanted to ask for ##1week## if somebody is making almost only maintenance edits, and wants articles to vanish if nobody argued within one week. Then it could be avoided to open the fly-out and choose an option with every edit.** Manually watching (//Default time period to watch a page that I manually add to my watchlist//)
# Provide //Special:Preferences// switch if new switch shall not appear (may be solved by personal CSS ##display:none## for more experienced users as first aid). Might be ##-1## in suggestion #1.** //Add pages and files I edit to my watchlist//
# Provide customized periods;** //Add pages I create and files I upload to my watchlist//
** //Add pages where I have performed a rollback to my watchlist//
* The preferred expiry should be pre-selected when:
** Using the watch star (aka manually watching)
** Editing a page (either wikitext or VisualEditor)
** Using the [[ https://www.mediawiki.org/wiki/Help:Watchlist_expiry#Watch_via_action%3Dwatch_%28available_for_desktop_%26_mobile_view%29 | action=watch ]] page
* If a page is already watched, we use the existing expiry and not the preference, either by editing arbitrary number of days and requesting ##40## days in suggestion #1ven if the preference is longer.
* Actions made through the [[ https://www.mediawiki.org/wiki/API:Main_page | Action API ]] should also follow the same rules when the `watchlist` parameter is set with either `preferences` (default) or `watch`
** If the `watchlistexpiry` parameter is used, or extend drop box by input field for number of daysthat takes precedence over the preferred expiry
* All of the above is true only if `$wgWatchlistExpiry` is also `true`.