Further expand the feature set Originally the Percolator feature set included basic PSM features such as the search engine score, the peptide length, and the charge state, which has currently been extended with features based on ML predictions. As PSM rescoring continues to evolve, we expect that features will be updated employing improved prediction models and that the currently used feature sets will be extended with novel features containing orthogonal information. For example, based on the isotope distribution it is possible to determine the number of Sulphur atoms present in the sample, indicating the number of cysteine residues .