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:…fabric is a quasiperiodic fabric with a small (1–5 km) characteristic wavelength, and hence arises from deformation of a layer of smaller effective mechanical thickness than the longer-wavelength (5 to >30 km) folds [Hansen and Willis, 1996, 1998; Phillips and Hansen, 1998; Ghent and Hansen, 1999].
Category: