How to use subnode description with port box

The packaging of a flow describes the way how to document input and output ports nicely with a "box" and datatypes...
Bildschirmfoto 2021-06-30 um 08.52.50

How can i add that kind of "box" in the subflow-description WYSIWYG Editor?
Bildschirmfoto 2021-06-30 um 08.54.12

Exactly as it says on the web page...

Or you can just use markdown