add explanation
add explanation

添加了几行解释element的注释
zhangaiping1/FEND_Note,jain0y/FEND_Note,Hellowor1d/FEND_Note,xiaojichao/FEND_Note,suen427/FEND_Note,rwang23/FEND_Note,ljwrer/FEND_Note,taoyingsong/FEND_Note,chowxiaojun/FEND_Note,Eriice/FEND_Note