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:Accordingly, almost all Arabidopsis D-type cyclins (CYCD4;2 being the only exception) contain at least one potential or poor PEST region (Menges et al. 2007) located N-terminal or C-terminal to the cyclin box, or even being present in both locations (Wang et al. 2004; Menges et al. 2007).
Category: