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