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 use of the intracellular dye carboxyfluorescein succinimidyl ester (CFSE) in proliferation assays has become an essential tool in mapping cellular division histories since its introduction in 1994 [17, 18, 19, 20, 23]–see also the recent surveys in [6, 12, 27].
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