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