Is it possible to search for events that do NOT have a tag set?

When submitting events, some of them may have a certain tag set (to an arbitrary value) whereas others will not have the tag at all. I would like to be able to write a query that would let me find events for which the tag was not set, i.e. it is absent.

It would be useful to know whether this is supported or I’d need to submit the tag for all events and for those events that should not have the tag set (the ones I’m trying to search for) set some dummy value to use later when querying (e.g. “unset”).