This function gets the bounding box of the primitives attached to a scene graph node s and recursively to all of its child nodes. The result node is connected to the six coordinates (x1, x2, y1, y2, z1, z2) which define the box.
When the function is executed (this happens for example when the function node is validated the first time after parsing an input file, or when there are changes in its parameter list at run time) the result node is created (or updated) and connected to the function node as its second node, so that the result can be accessed via the node selection operator [..] (or equivalently [2,..]).
s must be a scene graph node type.