generic type defs that can be used without #including a more specific header 

typedef int mbtk_bool_t;
typedef struct mbtk_backend_s mbtk_backend_t;
typedef struct mbtk_widget_s mbtk_widget_t;
typedef struct mbtk_window_s mbtk_window_t;
typedef struct mbtk_display_s mbtk_display_t;
typedef struct mbtk_style_s mbtk_style_t;
typedef struct mbtk_styleprop_s mbtk_styleprop_t; /* Opaque, declared within the style code */
typedef struct mbtk_widget_imp_s  mbtk_widget_imp_t;
typedef struct mbtk_event_s mbtk_event_t;
typedef struct mbtk_handler_s mbtk_handler_t;
typedef struct mbtk_htcb_s mbtk_callbacks_t;
typedef struct mbtk_pixmap_s mbtk_pixmap_t;

typedef struct mbtk_px_id_s {
  void *p;
  long l;
} mbtk_px_id_t;

typedef int mbtk_kw_t;
#define mbtk_kw_invalid ((mbtk_kw_t)0)

typedef union mbtk_font_id_u {
  long l;
  void *p;
} mbtk_font_id_t;

extern mbtk_font_id_t mbtk_invalid_font_id;
#define mbtk_is_font_id_invalid(fid) ((fid).l == -1)

/* opaque, backend-specific cursor handle type, used only as pointer */
typedef struct mbtk_mocu_s mbtk_mocu_t;

typedef enum mbtk_mocu_named_e {
  MBTK_MOCU_ARROW,      /* standard arrow */
  MBTK_MOCU_IBEAM,      /* I-beam, normally text editing */
  MBTK_MOCU_CROSSHAIR,
  MBTK_MOCU_HAND,
  MBTK_MOCU_HARROW,     /* horizontal arrow */
  MBTK_MOCU_VARROW      /* vertical arrow */
} mbtk_mocu_named_t;

typedef enum mbtk_event_handled_e {
  MBTK_EVENT_NOT_HANDLED = 0,
  MBTK_EVENT_HANDLED = 1
} mbtk_event_handled_t;