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