I'd like to be able to go into my Read books or TBR and look at all books that I haven't tagged with a tag beginning with e.g. "author-nationality-" or "set-in-" or "on-tbr-". I can manually pick all of the tags that start with that prefix, but it can get unwieldy with a lot of tags in a particular category, and I have to repeat that manual action any time I want to look at this filter again. In other apps, this often gets accomplished by being able to type in "on-tbr-*" into a filter box, and that would exclude ALL of the tags that start with that without me having to manually select the tags. Having this ability would greatly speed up a lot of the "let me tag all of the books with this new type of categorization scheme" tasks I've been doing lately so I can quickly see how many I have left to tag for a particular tag-set 😄