In the rich text editor:
@yuuxing
In a comment:
[yuuxing](https://chowlings.com/user/yuuxing)
For Names and Avatars:
In the rich text editor:
%yuuxing
In a comment:
[![yuuxing's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/yuuxing) [yuuxing](https://chowlings.com/user/yuuxing)