Section Header
    + name := GRP_TREE;
    - comment := "Tree representation";
Section Inherit
    + parent_gui:Expanded GUI;
Section Public
    + root_item:GUI_ITEM;
    + area_intern:GUI_INTERN;
    - bmp_tree:AREA <-
Creation
    - create_in f:AREA at (x,y:INTEGER) size (w,h:INTEGER) with itm:GUI_ITEM :SELF <-
    - make_in f:AREA at (x,y:INTEGER) size (w,h:INTEGER) with itm:GUI_ITEM <-
Line manager.
    - set_position rac:GUI_ITEM <-
Display.
    - draw (x0,y0:INTEGER) to (x1,y1:INTEGER) <-
Section Public
Event.
    - receive msg:EVENT <-
    + bmp_width_max:INTEGER;
    - update_position <-
    - open_group rac:GUI_ITEM at (x,y:INTEGER) :INTEGER <-
    - close_group rac:GUI_ITEM <-
    - last_group:ITM_GROUP;
    - get_group rac:GUI_ITEM at (x,y:INTEGER) to (px,py:INTEGER) :INTEGER <-