def declare_set(self, name, sep=os.pathsep):
self._declare_special(name, sep, SetVariable)<EOL>
Declare an environment variable as a set-like special variable.
This can be used even if the environment variable is not
present.

:param name: The name of the environment variable that should
             be considered set-like.
:param sep: The separator to be used.  Defaults to the value
            of ``os.pathsep``.