Spectral libraries are designed with an opposite approach: to unite the spectra and their interpretations into a single format. The significant difference, however, is that spectral libraries are intended to contain single or aggregated spectra that are deemed important, collated across potentially many experiments to form a reference set of spectra that may be used for downstream processing. Spectral libraries are, however, not intended to capture the complex output of mass spectrum processing pipelines (for which mzIdentML is designed).