docs: function (a1, a2, areUnique) {
          
          if (   !Arrays.isArrayLike(a1)
              || !Arrays.isArrayLike(a2)
              || a1.length !== a2.length )
              return false;
          
          var isSubset = Arrays._isSubsetOf(a1, a2);
          if (   isSubset
              && areUnique !== true )
              isSubset = Arrays._isSubsetOf(a2, a1);
          
          return isSubset;
      }