https://invisible-island.net/ncurses/man/
form_data(3x) Library calls form_data(3x)
       data_ahead, data_behind - test for off-screen data in given forms
       #include <form.h>
       bool data_ahead(const FORM *form);
       bool data_behind(const FORM *form);
       The function data_ahead tests whether there is off-screen data ahead in
       the given form.  It returns TRUE (1) or FALSE (0).
       The  function data_behind tests whether there is off-screen data behind
       in the given form.  It returns TRUE (1) or FALSE (0).
       These routines emulate the System  V  forms  library.   They  were  not
       supported on Version 7 or BSD versions.
       Juergen Pfeifer.  Manual pages and adaptation for new curses by Eric S.
       Raymond.
       curses(3x), form(3x)
ncurses 6.5                       2024-03-16                     form_data(3x)