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