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:PerRBS regulon genes includes katA, ahpCF, hemAXCDBL, mrgA, pfeT (formerly zosA), fur, and perR (Fuangthong et al., 2002; Guan et al., 2015).
Category: