The lossless JPEG recompression is a combination of VarDCT and some additional metadata. In fact, VarDCT should be considered as a (very large) superset of JPEG

The lossless JPEG recompression is a combination of VarDCT and some additional metadata. In fact, VarDCT should be considered as a (very large) superset of JPEG1 compression. The distinction between VarDCT and Modular in JPEG XL is relatively clear, but in reality VarDCT would still use modular encoding for various data anyway so it is hard to consider one without another. (Compare with Opus, which also uses two main mechanisms but mix them so well that they can't be really separated.)