In the rich text editor:
@roro989
In a comment:
[roro989](https://chowlings.com/user/roro989)
For Names and Avatars:
In the rich text editor:
%roro989
In a comment:
[![roro989's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/roro989) [roro989](https://chowlings.com/user/roro989)