Nodes of different colours represent the following:
Solid arrows point from a file to a file which it depends on. A file
is dependent upon another if the latter must be compiled before the former
can be.
program volatile_doctestuse stringifor_string_ttype(string)::astringastring='/bar/foo.tar.bz2'print'(L1)',astring%extension()//''=='.bz2'endprogram volatile_doctest