Where to define process categories and how to add them?

I have been looking at the documentation but can’t find any indication of how to do the following.
I wanted to add categories (or define them somewhere before adding) and looked at the properties tab in the modeler but and looked through the modeler application but could find nowhere to achieve this.
My goal is to be able to list processes containing user tasks and thought that by adding categories this would make it easier.
Appreciate any pointers as to how to achieve this.

The namespace property (of a process model) maps to the category property in the Flowable API.

Thank you very much.

When I changed the namespace from modeler, and download the xml, the namespace is always changed to http://flowable.io/test.
If I manually changed it, for example, “new_hire”, and publish it through the admin app, the category shows none.
The only way it works it do change the category through API.
I am using 6.6.0.
What is the right way to handle category?