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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def string(self) -> bytes: """The capabilities string without the enclosing square brackets."""

        if self._raw is not None:
            return self._raw
        self._raw = raw = BytesFormat(b' ').join(
            [b'CAPABILITY', b'IMAP4rev1'] + self.capabilities)
        return raw