code: function isOnlySiblingOfType(element, siblings) {
  			const siblingsOfType = siblings.filter(sibling => {
  				return (sibling.tagName === element.tagName);
  			});
  			return (siblingsOfType.length <= 1);
  		}
docs: Check whether an element is the only sibling of its type.
  @private
  @param {HTMLElement} element - An element to check siblings of.
  @param {Array} siblings - The siblings of the element.
  @returns {Boolean} Returns whether the element is the only sibling of its type.