pd_mutable
pd->pd_mutable = NULL;
pd->pd_mutable = nv;
pd->pd_mutable = nv;
data->pd_mutable = NULL;
data->pd_mutable = buf;
if ((pd->pd_flags & PD_F_NOCOPY) == 0 && pd->pd_mutable != NULL)
_PROP_FREE(pd->pd_mutable, M_PROP_DATA);