Question about GVBD and GVBG

[JalinWang]

    def get_alignment_loss(self, name, logits, x, align_logits):
        discriminator = getattr(self, name + "_discriminator")
        gvbg = getattr(self, name + "_gvbg")
        coeff = calc_coeff(self.iteration)
        bridge = gvbg(x)
        if self.opt.gvbg_weight > 0 and align_logits:
            logits = logits - bridge

        setattr(self, "loss_%s_gvbg" % (name), loss_gvbg)
        setattr(self, "loss_%s_gvbd" % (name), loss_gvbd)

Hi~I'm very confused by these two linear layers. They seem to be a logit-related trick, but I find no description in the paper/supp.
I would appreciate it if any explanation could be given on what they are used for.