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