code: function checkLevel(li){
              if(me.options.maxListLevel != -1){
                  var level = li.parentNode,levelNum = 0;
                  while(/[ou]l/i.test(level.tagName)){
                      levelNum++;
                      level = level.parentNode;
                  }
                  if(levelNum >= me.options.maxListLevel){
                      return true;
                  }
              }
          }
docs: 控制级数