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:, 2008; Pesch and Hülskamp, 2011) is an essential feature in all models explaining trichome patterning (Pesch and Hülskamp, 2009; Balkunde et al., 2010; Tominaga-Wada et al., 2011; Grebe, 2012).
Category: