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:Runx1 is expressed in IAHCs of mouse (North et al., 2002), Xenopus (CiauUitz et al., 2000) zebrafish (Lam et al., 2010) and chicken (Richard et al., 2013) embryo and is required for their proper emergence (Chen et al., 2009; North et al., 1999) during EHT (Chen et al., 2009).
Category: