One important feature of SpectraFit to know is the support of lmfit's string expression for distribution models. Rather than setting specific ranges and initial values for distribution models, the lmfit-solver can be instructed through usersupplied expression to apply constraints to the fitting model. This feature may seem abstract, but it can be beneficial for maintaining a constant branching ratio for the amplitude (intensity) of L3-and L2-peaks when fitting L-edge XAS. Another scenario where utilizing an automatized user-supplied expression is beneficial is during global fitting routines, where the peak energies between spectra must remain constant. SpectraFit's global fitting routine uses the initial user input to generate shared fitting parameters through internally auto-generated expressions. These expressions ensure that each spectrum is fitted with the appropriate set of distributions. By utilizing the expression, the peak intensity (amplitude) and broadening can be confirmed, and the position (energy) value is frozen based on the expression's internal dependency. Previously published results demonstrated the need for this routine, for example, for fitting RIXS, time-resolved UV-visible absorption measurements, or characterizing enzyme kinetics. For this study, complexes 1 and 2 illustrate how this routine works, following previously published methods.