In the rich text editor:
@Rxtt3n
In a comment:
[Rxtt3n](https://chowlings.com/user/Rxtt3n)
For Names and Avatars:
In the rich text editor:
%Rxtt3n
In a comment:
[](https://chowlings.com/user/Rxtt3n) [Rxtt3n](https://chowlings.com/user/Rxtt3n)