def _fix_value(self, value):
        """
        Return a cleaned version of a value
        according to the specification:
        > Char	   ::=   	#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]

        See https://www.w3.org/TR/xml/#charsets

        :param value: a value to clean
        :return: the cleaned value
        """
        if not self.__charrange or not self.__replacement:
            self.__charrange = re.compile('^[\u0020-\uD7FF\u0009\u000A\u000D\uE000-\uFFFD\U00010000-\U0010FFFF]*$')
            self.__replacement = re.compile('[^\u0020-\uD7FF\u0009\u000A\u000D\uE000-\uFFFD\U00010000-\U0010FFFF]')

        # Reading string until \x00. This is the same as aapt does.
        if "\x00" in value:
            self.packerwarning = True
            log.warning("Null byte found in attribute value at position {}: "
                        "Value(hex): '{}'".format(
                value.find("\x00"),
                binascii.hexlify(value.encode("utf-8"))))
            value = value[:value.find("\x00")]

        if not self.__charrange.match(value):
            log.warning("Invalid character in value found. Replacing with '_'.")
            self.packerwarning = True
            value = self.__replacement.sub('_', value)
        return value
Return a cleaned version of a value
        according to the specification:
        > Char	   ::=   	#x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]

        See https://www.w3.org/TR/xml/#charsets

        :param value: a value to clean
        :return: the cleaned value