+ * DATA ORGANISATION :
+ * tint2 define one panel per monitor. And each panel have a tree of Area (nodes).
+ * The root of the tree is Panel.Area. And task, clock, systray, taskbar,... are nodes.
+ *
+ * 'panel_items' parameter (in config) define the list and the order of nodes in tree's panel.
+ * 'panel_items = SC' define a panel with just Systray and Clock.
+ * So the root Panel.Area will have 2 childs (Systray and Clock).
+ *
+ * The tree allow to browse panel's objects from background to foreground and from left to right.
+ * The position of each node/Area depend on parent's position and brothers on the left.
+ *
+ * DRAWING EVENT :
+ * In the end, redrawing an object (like the clock) could come from an external event (date change)
+ * or from a layering event (size or position change).
+ *
+ * DRAWING LOOP :