Section Header
    + name := G_GROUP;
    - author := "Sonntag Benoit (bsonntag@loria.fr)";
    - comment := "Group elements for GUI.";
Section Inherit
    + parent_area:Expanded AREA;
    + parent_g_expr:Expanded G_EXPR;
Section Public
    + root:G_EXPR;
Width / Height
    - width_min:INTEGER <-
    - height_min:INTEGER <-
Creation.
    - create elt:G_EXPR :SELF <-
    - make elt:G_EXPR <-
Update position.
    - set_position rac:AREA at (x,y:INTEGER) <-
    - set_position rac:AREA at (x,y:INTEGER) size (w,h:INTEGER) <-
Display.
    - draw (x0,y0:INTEGER) to (x1,y1:INTEGER) <-
    - draw_slave bmp:ABSTRACT_BITMAP from (x0,y0:INTEGER) to (x1,y1:INTEGER) <-
    - refresh <-
    - delete <-