def parse(self, xastr):
        # type: (bytes) -> None
        '''
        Parse an Extended Attribute Record out of a string.

        Parameters:
         xastr - The string to parse.
        Returns:
         Nothing.
        '''
        if self._initialized:
            raise pycdlibexception.PyCdlibInternalError('This XARecord is already initialized!')

        (self._group_id, self._user_id, self._attributes, signature, self._filenum,
         unused) = struct.unpack_from(self.FMT, xastr, 0)

        if signature != b'XA':
            raise pycdlibexception.PyCdlibInvalidISO('Invalid signature on the XARecord!')

        if unused != b'\x00\x00\x00\x00\x00':
            raise pycdlibexception.PyCdlibInvalidISO('Unused fields should be 0')

        self._initialized = True
Parse an Extended Attribute Record out of a string.

        Parameters:
         xastr - The string to parse.
        Returns:
         Nothing.