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:vinifera (P28343, Coutos-Thevenot et al., 2001; Giorcelli et al., 2004; Zhu et al., 2004) that have been successfully used in gene transfer experiments.
Category: