* respectively. Any other non-ASCII characters appearing in the input will be preserved in the
   * output.
   *
   * <p>This escaper does not treat surrogate pairs specially and does not perform Unicode
   * validation on its input.
   */
  @SuppressWarnings("EscapedEntity") // We do mean for the user to see &#x9;" etc.

    // Test all escapes
    assertEquals(
        "a&quot;b&lt;c&gt;d&amp;e&quot;f&apos;", xmlAttributeEscaper.escape("a\"b<c>d&e\"f'"));
    // Test '\t', '\n' and '\r' are escaped.
    assertEquals("a&#x9;b&#xA;c&#xD;d", xmlAttributeEscaper.escape("a\tb\nc\rd"));
  }

  // Helper to assert common properties of xml escapers.
  static void assertBasicXmlEscaper(