'Implementation-dependent helper function.
Will be passed a match object corresponding to the interpolation
key we just found (e.g., "%(foo)s" or "$foo"). Should look up that
key in the appropriate config file section (using the ``_fetch()``
helper function) and return a 3-tuple: (key, value, section)
``key`` is the name of the key we\'re looking for
``value`` is the value found for that key
``section`` is a reference to the section where it was found
``key`` and ``section`` should be None if no further
interpolation should be performed on the resulting value
(e.g., if we interpolated "$$" and returned "$").'

def _parse_match(self, match):

    raise NotImplementedError()
