Clojurians Log v2

(I'm not sure if there's a better place for specmonstah questions; please direct me elsewhere if there is.) I'm using the (superb) specmonstah library to generate a big chunk of test data. One can use :constraints {:some_field #{:uniq}} to ensure a particular field is unique. however, sometimes the field is only unique within some more limited namespace. is there any way to write a custom constraint? I want a field that's unique among all those that share the same parent (another field).