docs: function mergeQueries(a,b) {
      for(var k in b) {
          if(k in a) {
              if(k === '$and') {
                  a[k] = a[k].concat(b[k])
              } else {
                  var andOperandA = {}; andOperandA[k] = a[k]
                  var andOperandB = {}; andOperandB[k] = b[k]
                  var and = {$and:[andOperandA,andOperandB]}
                  delete a[k]
                  mergeQueries(a,and)
              }
          } else {
              a[k] = b[k]
          }
      }
  }