def _has_xml_encode(self, content):
        """Check XML encoding."""

        encode = None

        m = RE_XML_START.match(content)
        if m:
            if m.group(1):
                m2 = RE_XML_ENCODE.match(m.group(1))

                if m2:
                    enc = m2.group(2).decode('ascii')

                    try:
                        codecs.getencoder(enc)
                        encode = enc
                    except LookupError:
                        pass
            else:
                if m.group(2):
                    enc = 'utf-32-be'
                    text = m.group(2)
                elif m.group(3):
                    enc = 'utf-32-le'
                    text = m.group(3)
                elif m.group(4):
                    enc = 'utf-16-be'
                    text = m.group(4)
                elif m.group(5):
                    enc = 'utf-16-le'
                    text = m.group(5)
                try:
                    m2 = RE_XML_ENCODE_U.match(text.decode(enc))
                except Exception:  # pragma: no cover
                    m2 = None

                if m2:
                    enc = m2.group(2)

                    try:
                        codecs.getencoder(enc)
                        encode = enc
                    except Exception:
                        pass

        return encode
Check XML encoding.