In her case it’s for her email backlog and the idea is to pick two points in time – like last Christmas to last Tuesday – and filter her inbox to only show messages before Christmas and after Tuesday. I.e., everything except that particular date range. She bookmarks that search and treats it as her inbox – a manageable mix of ancient things and new things. When and only when that search is empty, she squeezes the date range a little tighter in both directions.
(-is:chat -is:snoozed (after:2020/03/17 OR before:2019/12/25) OR is:starred OR is:unread) AND in:inbox
I like how it incorporates redqueening. Part of squeezing down the backlog is keeping up with the current inflow. It’s not strict isolation of the backlog but it achieves the important part of that: creating a backlog that isn’t being added to as new items arrive. The backlog is everything in the date range which is getting inexorably squeezed down until it’s gone.