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:…cloning of the GABAB(1) gene, a second, structurally similar,
member of the GABAB receptor family: the GABAB(2) subunit was described concomitantly by a number of research groups (Jones et al. 1998; Kaupmann et al. 1998a; Kuner et al. 1999;
Martin et al. 1999; Ng et al. 1999; White et al. 1998).
Category: