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 current staging system for non-small cell lung cancer (NSCLC) is tumor-node-metastasis (TNM) staging,(2) which provides only a definition of the anatomic extent of the neoplasia: size, location, and extent of the primary lesion; presence and location of the locoregional lymph node metastasis; and systemic metastatic disease.
Category: