Jacob’s Ladder seems like an approach to try and reach the “divine” functional. For DFT it goes in the order of LDA, GGA, meta-GGA, hybrid functionals for treating the exchange part exactly, and lastly something to refine the correlation part. As someone who barely understood what the xc-functional did, now I can see the usefulness of the DFT method in contrast to post-HF methods for specific use cases.