Well since the original answer someone got drunk and gave me source code access, so how about we allow
Your search can now be performed like this:
[myTag] or [myOtherTag]closed:0 answers:0, this would return results containing either tag. Here are a few more examples:
[myTag] or [myTag2] or [myTag3] closed:0 answers:0 - any of the 3 tags
[myTag] or [myTag2] [myTag3] closed:0 answers:0 - either of the first 2 and the 3rd tag
[myTag] or [myTag2] [myTag3] or [myTag4] closed:0 answers:0 - either of the first 2 and either of the last 2
(A || B) && (C || D)
Original: Just throwing this option out there, certain tags could be reserved for this purposed: e.g.
[protected], etc. (Maybe these are already reserved?). The search could handle these appropriately on the back-end as special filters.
I'm not sure that this would be the best approach, but it would be a way to keep the syntax simpler overall.
Alternatively, you could allow counts to be put in, e.g.
[answers:1], in this case
[unanswered] would be a simple alias for
[answers:0], allowing more flexibility overall...maybe this is over-complicating things though, I'm not sure how many would use this feature...