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 addition, gstA harbours sequences upstream of the initial ATG with similarity to the xenobiotic (XRE) and antioxidant responsive elements (ARE) involved in regulation of mammalian GSTs (Hayes and Pulford, 1995; Rushmore et al., 1991; Rushmore and Pickett, 1993).
Category: