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