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:5 mm,[6,13] absence of communications of both SIEVs crossing the abdominal midline,[6,13] absence of direct communications by perforators between the SIEV and the deep inferior epigastric vein (DIEV),[6] number of perforators of the flap,[5] and subcutaneous tissue thickness.
Category: