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