def scan(self, folder, sub=None, next_=None):
        """ Request immediate rescan of a folder, or a specific path within a
        folder.

            Args:
                folder (str): Folder ID.
                sub (str): Path relative to the folder root. If sub is omitted
                    the entire folder is scanned for changes, otherwise only
                    the given path children are scanned.
                next_ (int): Delays Syncthing's automated rescan interval for
                    a given amount of seconds.

            Returns:
                str
        """
        if not sub:
            sub = ''
        assert isinstance(sub, string_types)
        assert isinstance(next_, int) or next_ is None
        return self.post('scan', params={'folder': folder,
                                         'sub': sub,
                                         'next': next_})