Not sure to have the exact knowledge but from what I've understood, it's a mechanism that makes some parts move in synch while moving the master part, for example changing the shape of the breasts on the character introduces the same changes in the corresponding part of the cloth.

I tested this yesterday on a Sasha-16, which is a Vic4 weight-mapped but it continued to follow the changes on the cloth level, and it does the same with a classic Vic4

But that's not something I'm completely at ease with. When I need a similar effect, I use NGM, which lets me redefine with ease the shape of the breasts, as some clothes aren't really cooperative at this level.

𝒫𝒽𝓎𝓁

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