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