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:In all strains, Pex3pmRFP could be found in the 20KgP fraction, which contains both mature and some forms of immature peroxisomes (Tam et al., 2003; Vizeacoumar et al., 2003, 2004), and in the 200KgP fraction containing vesicular structures.
Category: