why is there a 0 in this function```    SigHashType withFork(bool fork = true) const {
        return SigHashType((sigHash & ~SIGHASH_FORKID) |
                           (fork ? SIGHASH_FORKID : 0));
    }``` Avoid using the following keywords: sighashtype((sighash, fork, sighash_forkid, sighashtype
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