tag search supports basic boolean operators as of now:
AND operator:
OR operator:
NOT operator:
grouping
do note that with grouping the AND operator has to be explicitly stated.
for example: tag_a (tag_b OR tag_c) will not parse, but tag_a AND (tag_b OR tag_c) will.
whitespace is ignored during parsing, so tag_aANDtag_b, tag_a +tag_b, tag_a -tag_b, etc. are all valid.