code: function selectorBlockHandler(element) {
      if (element.type === 'Selector') {
          const name = []
          let discard = false
          element.children.forEach(e => {
              switch (e.type) {
                  case "ClassSelector":
                      name.push("." + e.name);
                      break;
                      //not support for now
                  case "Combinator":
                      name.push(e.name);
                      discard = true
                      return null
                  case "TypeSelector":
                      name.push(e.name);
                      break;
                  case "IdSelector":
                      //not support for now
                      name.push("#" + e.name);
                      discard = true
                      return null
                  case "WhiteSpace":
                      name.push(" ");
                      break
                  default: {
                      // console.warn('unknown selector type:', e)
                      discard = true
                      return null
                  }
              }
          })
          if (!discard)
              return name.join("")
          else return null
      }
  }
docs: handle with selector part in node's structure
  @param element node to be searched
  @return {*}