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:…cells of diverse tissue types may suggest that this marker is indicative of a general precursor cell rather than one specifically committed to a neural lineage (About et al., 2000; Ha et al., 2003; Mokry and Nemecek, 1998; Niki et al., 1999; Sejersen and Lendahl, 1993; Zulewski et al., 2001).
Category: