Thank you very much for this, one additional question.  In testing this looks like it logs any change to a check box, so if someone opted into a new option, rather than opting out, it still logs it.  Is there a way to differentiate between a check and an uncheck and log those separately? Thanks!

I am trying to set up a Landing Page to manage a set of subscriptions, and would like to have a subpage on confirm that shows a message "Thank you, you have opted out of (Subscription X)".  How do I pass a value for each of the check boxes from the Landing Page to a Sub Page? Looking at the document...