Nodes of different colours represent the following:
Solid arrows point from a submodule to the (sub)module which it is
descended from. Dashed arrows point from a module or program unit to
modules which it uses.
program volatile_doctestuse stringifor_string_ttype(string)::astringastring='/bar/foo.tar.bz2'print'(L1)',astring%extension()//''=='.bz2'endprogram volatile_doctest