/sys$common/syshlp/helplib.hlb CC, Run-time functions, overlay  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Curses Screen Management routine that superimposes win1 on win2.
  The function writes the contents of win1 that will fit onto win2
  beginning at the starting coordinates of both windows.  Blanks on
  win1 leave the contents of the corresponding space on win2
  unaltered.  The overlay function copies as much of the window's box
  as possible.

  Syntax:

       #include <curses.h>

       int overlay(WINDOW *win1, WINDOW *win2);