@Override
    public void characters(char[] ch, int start, int length) throws SAXException {
        filter(ch, start, length, charactersOutput);
    }
@Test
    public void testInvalidCharacters() throws SAXException {
        safe.characters("ab\u0007".toCharArray(), 0, 3);
        safe.characters("a\u000Bc".toCharArray(), 0, 3);
        safe.characters("\u0019bc".toCharArray(), 0, 3);
        assertEquals("ab\ufffda\ufffdc\ufffdbc", output.toString());
    }