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