code: function (overlayName, modelName) {
      var key = (overlayName || BASE_OVERLAY) + '#' + modelName;
      if (!this.instances[key]) {
        this.instances[key] = DevFixturesFixtures.create({
          modelName:   modelName,
          overlayName: overlayName
        });
      }
      return this.instances[key];
    }
docs: Get the instance for given overlay name and model name
  
  @method for
  @param {string} overlayName
  @param {string} modelName
  @return {DevFixturesFixtures}