i plan to extend the Matukio booking form by a custom booking field, a checkbox (Register for Newsletter). This part is done and no problem.
However: If said box is checked, I want to register the email/name of the person with the Joomla Newsletter component JNews.

My question is: What's the best way to access the booking form and check whether the checkbox was checked? Does the booking form provide any plugin hook where i can insert a dedicated data handler for this? Or do i need to modify the core Matukio booking form handler code?