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:CR1‐like Superfamily Phylogenetic Analyses Vertebrate nucleotide sequences belonging to the CR1‐like retrotransposon superfamily were retrieved using Repbase Update (Jurka et al., 2005) as well as through systematic BLASTanalysis of public databases accessible from NCBI (http://blast.ncbi.nlm.nih. gov/Blast.cgi) and Ensembl (http://www.ensembl.org/Multi/blastview) servers, resulting in a set of 844 vertebrate nucleotide sequences.
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