I have been digging more into this problem. It appears to be either surprisingly complex or just buried deeply within the query model architecture of Nuxeo. I would be very interested in seeing how it could be solved. It appears as if a right extension at the right extension point likely with no code and just XML is what I need.

The filtering of tags is defined by dcSubjectsDirectoryTree. This in turn uses query model FILTERED_DOCUMENTS on the dc_subjects field (part of subtopic). So the original question can be rephrased: how does one force FILTERED_DOCUMENTS query model to use AND operator instead of OR.

Tom

So this complicates things a bit with FILTERED_DOCUMENT. I get this in the log:

Query models are deprecated as of Nuxeo 5.4 and will be removed for Nuxeo 6.0: the query model 'FILTERED_DOCUMENTS' should be upgraded to use content views