Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…succinylation (Zhang et al. 2011; Park et al. 2013; Weinert et al. 2013b) in organisms from humans to bacteria, malonylation (Peng et al. 2011) and glutarylation (Tan et al. 2014) in eukaryotes, and propionylation in bacteria (Okanishi et al. 2014) were recently revealed as prevalent PTMs.
Category: