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