docs: function(after, before, inc, iterator) {
          var args = {
                  before: before,
                  after: after,
                  inc: inc
              }
  
          if (iterator) {
              return this._iter(
                  new CallbackIterResult('between', args, iterator));
          } else {
              var result = this._cacheGet('between', args);
              if (result === false) {
                  result = this._iter(new IterResult('between', args));
                  this._cacheAdd('between', result, args);
              }
              return result;
          }
      }