def _jsnp_unescape(jsn_s):
    """
    Parse and decode given encoded JSON Pointer expression, convert ~1 to
    / and ~0 to ~.

    .. note:: JSON Pointer: http://tools.ietf.org/html/rfc6901

    >>> _jsnp_unescape("/a~1b")
    '/a/b'
    >>> _jsnp_unescape("~1aaa~1~0bbb")
    '/aaa/~bbb'
    """
    return jsn_s.replace('~1', '/').replace('~0', '~')