expect:
        //	Char	   ::=   	#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]
        //	/* any Unicode character, excluding the surrogate blocks, FFFE, and FFFF. */
        !XmlValidation.isLegalCharacter(character)

        where:
        character      | _
        0x8            | _
        0xb            | _
        0xf            | _
        (0x20 - 1)     | _
        (0xd7ff + 1)   | _

        }
    }

    private void writeCDATA(int ch) throws IOException {
        if (needsCDATAEscaping(ch)) {
            writeRaw("]]><![CDATA[>");
        } else if (!XmlValidation.isLegalCharacter(ch)) {
            writeRaw('?');
        } else if (ch <= 0xffff && XmlValidation.isRestrictedCharacter((char) ch) || Character.charCount(ch) == 2) {
            writeRaw("]]>");
            writeCharacterReference(ch);

     *
     * @link https://www.w3.org/TR/REC-xml/#charsets
     * @param c codepoint
     * @return true when the codepoint is a valid XML char
     */
    public static boolean isLegalCharacter(final int c) {
        if (c == 0x9 || c == 0xA || c == 0xD) {
            return true;
        } else if (c < 0x20) {
            return false;
        } else if (c <= 0xD7FF) {
            return true;