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:…by Cold Spring Harbor Laboratory Press for the RNA Society 721
vivo UV cross-linking does not promote formation of covalent bonds between proteins (Pashev et al. 1991; Suchanek et al. 2005), and hence offers an approach to “freeze” directly binding RBPs to RNAs in vivo for subsequent…
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