Curses Menu Library (libmenu, -lmenu)
The menus library provides a terminal independent menu
  system using the curses(3)
  library. Before using the menus functions the terminal
  must be set up by curses(3)
  using the initscr() function or similar. Programs
  using menus functions must be linked with the
  curses(3) library.
The menus library provides facilities for
    defining menu items, placing a menu on the terminal screen, assign pre- and
    post-change operations and setting the attributes of both the menu and its
    items.
Any function returning a string pointer will return NULL if an error occurs.
  Functions returning an integer will return one of the following:
  - E_OK
- The function was successful.
- E_SYSTEM_ERROR
- There was a system error during the call.
- E_BAD_ARGUMENT
- One or more of the arguments passed to the function was incorrect.
- E_POSTED
- The menu is already posted.
- E_CONNECTED
- An item was already connected to a menu.
- E_BAD_STATE
- The function was called from within an initialization or termination
      routine.
- E_NO_ROOM
- The menu does not fit within the subwindow.
- E_NOT_POSTED
- The menu is not posted.
- E_UNKNOWN_COMMAND
- The menu driver does not recognize the request passed to it.
- E_NO_MATCH
- The character search failed to find a match.
- E_NOT_SELECTABLE
- The item could not be selected.
- E_NOT_CONNECTED
- The item is not connected to a menu.
- E_REQUEST_DENIED
- The menu driver could not process the request.
curses(3),
  menu_attributes(3),
  menu_cursor(3),
  menu_driver(3),
  menu_format(3),
  menu_hook(3),
  menu_item_current(3),
  menu_item_name(3),
  menu_item_new(3),
  menu_item_opts(3),
  menu_item_userptr(3),
  menu_item_value(3),
  menu_item_visible(3),
  menu_items(3),
  menu_mark(3),
  menu_new(3),
  menu_opts(3),
  menu_pattern(3),
  menu_post(3),
  menu_userptr(3),
  menu_win(3)
This implementation of the menus library does depart in behaviour subtly from
  the original AT & T implementation. Some of the more notable departures
  are:
  - unmark
- The original implementation did not have a marker for an unmarked field
      the mark was only displayed next to a field when it had been marked using
      the REQ_TOGGLE_ITEM. In this implementation a separate marker can be used
      to indicate an unmarked item. This can be set using set_menu_unmark
      function. There is no requirement for the mark and unmark strings to be
      the same length. Room will be left for the longest of the two. The unmark
      string is optional, if it is not set then menus defaults to the old
      behaviour.
- item marking
- In the original implementation the current item was considered selected
      and hence had the mark string displayed next to it. This implementation
      does not do this because the Author considers the effect too confusing.
      Especially in the case of a multiple selection menu because there was no
      way to tell if the current item is selected or not without shifting off of
      it. Since the current item is displayed using the foreground attribute it
      was deemed unnecessary to also display the mark string against the current
      item.
The option O_RADIO and the function
    item_selected() are NetBSD
    extensions and must not be used in portable code.