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