def __call__(relative=0, *args, **kw):
    """ Return URL of the site, as a string.

        o If 'relative' is True, return only the "path" portion of the site
          object's URL; otherwise, return the absolute URL

        o In either case, the returned path respects virtual hosting.

        o The site is the parent of the tool.

        o Permission:  Public
        """
