In the case of a regular fit, the correlation analysis can indicate trends of overfitting, which can be double-cross-checked with the Bayesian Information Criterion (BIC) and the Akaike Information Criterion (AIC). The BIC and AIC are calculated by the lmfit package and are based on the fit statistics. Opposite potential use cases for SpectraFit could be the analysis of RIXS , and XMCD spectra, where high correlation coefficients can help, for example, to resolve the Zhang-Rice singlet, d-d excitation, and charge-transfer contributions in time-resolved RIXS , compare the optical spectra of magnetic circular dichroism (MCD) with 2p3d RIXS , or the separation between for positive and negative helicity in XMCD.