In the rich text editor:
@XiaoNiao
In a comment:
[XiaoNiao](https://chowlings.com/user/XiaoNiao)
For Names and Avatars:
In the rich text editor:
%XiaoNiao
In a comment:
[](https://chowlings.com/user/XiaoNiao) [XiaoNiao](https://chowlings.com/user/XiaoNiao)