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='say all Hello WorLD!'print'(L1)',astring%chars()=='say all Hello WorLD!'endprogram volatile_doctest