page -- an integer for the page number used to calculate the next page
result -- an integer for the next page number

The callback function used by the gtk:assistant-set-forward-page-func function to know which is the next page given a current one. It is called both for computing the next page when the user presses the forward button and for handling the behavior of the last button. The gtk:assistant implementation is deprecated since 4.10. This widget will be removed in GTK 5.