_getGalleryDOMElements(galleryElement) {
    var _this$options3, _this$options4;

    if ((_this$options3 = this.options) !== null && _this$options3 !== void 0 && _this$options3.children || (_this$options4 = this.options) !== null && _this$options4 !== void 0 && _this$options4.childSelector) {
      return getElementsFromOption(this.options.children, this.options.childSelector, galleryElement) || [];
    }

    return [galleryElement];
  }
Get array of gallery DOM elements,
based on childSelector and gallery element.

@param {HTMLElement} galleryElement
@returns {HTMLElement[]}