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