In the rich text editor:
@Drex_Test
In a comment:
[Drex_Test](https://chowlings.com/user/Drex_Test)
For Names and Avatars:
In the rich text editor:
%Drex_Test
In a comment:
[](https://chowlings.com/user/Drex_Test) [Drex_Test](https://chowlings.com/user/Drex_Test)