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