This version of the code includes the planet formation process in the dust and metal evolution. This includes three new parameters (f_disc, f_wind, f_debris) which account for the fact that not all metals and dust are lost per unit star formation (classical astration) due to the planet formation process which can return some material back to the ISM.
All the equations and rationale can be found in Forgan et al 2017, MNRAS 10.1093/mnras/stx2162