directive: 目的是給DOM元素添加自定義行為，可以和Component class一樣，實作life cycle hooks：
Can’t bind to ‘cxFocusConfig’ since it isn’t a known property of ‘div’. ("
答案：
you cant use input/output outside component / directive tag
正确做法？
Hello
so it seems the name of selector and input are kept the same ON PURPOSE?
I think for small directives (single responsibility and single input) its simplified usage