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