code: def path_constant(self, name, value):
          
          assert is_iterable_typed(name, basestring)
          assert is_iterable_typed(value, basestring)
          if len(value) > 1:
              self.registry.manager.errors()("path constant should have one element")
          self.registry.current().add_constant(name[0], value, path=1)
docs: Declare and set a project global constant, whose value is a path. The
          path is adjusted to be relative to the invocation directory. The given
          value path is taken to be either absolute, or relative to this project
          root.