In the rich text editor:
@Xaunus
In a comment:
[Xaunus](https://www.worldofgaia.org/user/Xaunus)
For Names and Avatars:
In the rich text editor:
%Xaunus
In a comment:
[](https://www.worldofgaia.org/user/Xaunus) [Xaunus](https://www.worldofgaia.org/user/Xaunus)