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