Section Header
    + name := PLAN;
    - comment := "Sub structure for WINDOW.";
    - version := 1;
Section Inherit
    - parent_object:OBJECT :=
Section Public
+--------------------+
| (x0,y0) |
| X------------|.........+
| | / / / / / /| :
| |/ / / / / / | :
| | / PLAN / /| :
| |/ / / / / / | :
| | / / / / / /| :
| +------------X.........+
| (x1,y1)
| |
+--------------------+
    + is_x:BOOLEAN;
    + is_y:BOOLEAN;
    + level:INTEGER;
    + window:AREA;
Limit.
    + x0:LIMIT_X;
    + x1:LIMIT_X;
    + y0:LIMIT_Y;
    + y1:LIMIT_Y;
Link.
    + next:PLAN;
    + prev:PLAN;
Section Public
    - make win:AREA <-
    - create win:AREA :PLAN <-
    - remove old_root:PLAN :PLAN <-
    - display <-
    - dec_level <-
    - inc_level <-
    - set_x0 new:LIMIT_X <-
    - set_y0 new:LIMIT_Y <-
    - set_x1 new:LIMIT_X <-
    - set_y1 new:LIMIT_Y <-
    - set_level new:INTEGER <-
    - set_next new:PLAN <-
    - set_prev new:PLAN <-
    - active_y <-
    - desactive_y <-
    - active_x <-
    - desactive_x <-