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 5 2.3 kb enhancer region (chr2: 19351717-19354014) was cloned into the BgEGFP reporter vector (Lumpkin et al., 2003) to generate 2.3Ptf1a-GFP or a nuclear lacZ reporter gene with the minimal promoter of the rat Ela1 gene to generate 2.3Ptf1a-lacZ (Masui et al., 2008).
Category: