text: // 형제노드 위치상의 순서를 반환하는 함수
  
  export default function index(target) {
    let explorationCount = 0,
        prevElement = target.previousElementSibling,
        firstTargetTagName = target.tagName;
    
    while(prevElement !== null) {
      if(prevElement.tagName !== firstTargetTagName) break;
      explorationCount++;
      prevElement = prevElement.previousElementSibling;
    }
    
    return explorationCount;
  }
  