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:Several sample preparation methods have been employed for the elemental analysis of wines, including direct dilution by factors ranging from one to 10, UV-assisted digestion, and open or closed vessel acid digestion assisted by microwave radiation [4,6–12].
Category: