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:Three DDR2 binding sites have been mapped on the collagen triple helix by us(26) for collagen type 1 and by others using the collagen toolkit for collagen type 2.(27) All of the three reported binding sequences are conserved in the α1 chain of collagen types 1, 2 and 3.
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