It seems @srunderwood did not have any tag in Zotero, but relied on a negative search. “NOT” searches are a standard Boolean operator and it is not unusual to incorporate it into one’s workflow. For instance, I would love to be able to search for items with the tag TAIWAN that are not tagged INDIGENOUS. Many of my papers are about indigenous Taiwanese, but sometimes I’m looking for something that is about Taiwan but which is not related to indigenous issues. Excluding them from the search would save me a lot of time.