def __init__(self, urlaccessor, doc=None, dolater=None, keep=None):
        if doc is not None:
            self.__doc__ = doc
        self.urlaccessor = urlaccessor
        if dolater is None:
            dolater= []
        self.dolater = dolater
        if keep is None:
            keep = []
        self._keep = keep
A Proto like object for abstractly specifying urls in stan trees.
dataset/ETHPy150Open twisted/nevow/nevow/url.py/URLOverlay.__init__