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:, 2009), are most abundant on endosomes undergoing the early-to-late transition (Rojas et al., 2008; Cullen and Korswagen, 2012; van Weering et al., 2012).
Category: