Doc: Howto use "stillprocessing"

[PhMemmel]

Sorry to open an issue for that, but it's a documentation issue for me :-)

I'm wondering what "stillprocessing: the step still wants to process the course and is responsible for rendering the site." actually means or better: how to use this.

My use case would be: I want a user to do an interactive action. But I don't want the action to immediately take place when the user hits the button, but I want the user to get redirected to another site (which servers additional explanations what he has to do etc.) On this page he/she finally hits a button which should trigger the real action I want the plugin step to execute.

Currently I have an action defined in handle_interaction in my step subplugin. If the user hits the button he sends this action and I just call a redirect to my custom site from the handle_interaction method which means I exit the handle_interaction method before I can return anything (especially I cannot return step_interactive_response::still_processing(). After the user has confirmed the action I manually call process_proceed or - if the action fails - process_rollback to "finalize" this step which I feel is not the right way to do, or is it? How do I use the step_interactive_response::still_processing() then?

Can you give me an example on how I use step_interactive_response::still_processing() return value of handle_interaction to be able to deal with the use case of having my own site triggering the real action? Or is this a complete different type of use case this option is trying to address?

Thank you very much in advance!