code: function(mCons, vCons, k){
              var nCons = {}; // the final nested constraints
              
              // if there are per-key constraints for k, add them all
              if(validate.isObject(mCons[k])){
                  nCons = validateParams.extendObject({}, mCons[k]);
              }
              
              // loop through each universal constraint and merge as appropraite
              if(vCons){
                  Object.keys(vCons).forEach(function(vn){
                      // only add non-clashing universal constraints
                      if(!nCons[vn]){
                          nCons[vn] = vCons[vn];
                      }
                  });
              }
              
              // return the merged constraints
              return nCons;
          }
docs: a private inner function for merging per-key and universal constraints