An Internet Protocol Version 4 address. This requires no additional argument. It
is checked whether or not the buffer has the form a.b.c.d, where a,b,c and d are
numbers between 0 and 255. Trailing blanks in the buffer are ignored. The address
itself is not validated. Please note that this is an ncurses extension. This
field type may not be available in other curses implementations.
It is possible to set up new programmer-defined field types. See the
form_fieldtype(3X) manual page.