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 13.4Ptf1a5 -lacZ construct contains chr2:19353922-19367481, and the 15.6Ptf1a5 -lacZ construct contains chr2:19351717-19367481 placed 5 to a lacZ reporter gene (Masui et al., 2008).
Category: