Except they don’t really have it. It’s a claim they try to back up by retroactively creating accomplished facts, like their artificial islands and this floating barrier. This would require their claims to be legitimate though, which they aren’t, neither under maritime law nor international recognition. It was as made up in 1946 as it is now, for both the PRC and the ROC. The only clear indicator of ownership in the South China sea is the EEZ, which doesn’t give China anything close to its claims.