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 petunia, the elucidation of MADS box protein dimer and higher order complex formation is well under way (Ferrario et al., 2003; Immink et al., 2003), and there is an extensive body of research that has used ectopic expression and/or cosuppression studies to identify floral developmental…
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