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:The method for the WRAIR ChE assay has been previously described (U.S. Patent No. 6,746,850, Feaster et al., 2004; Gordon et al., 2005; Haigh et al., 2008).
Category: