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:N-terminal mutants affect HR elicitation but not SAR
The active domains for HR elicitation in harpinPss and harpinPph from Pseudomonas strains reside in the C-terminal region (Arlat et al. 1994; Lee et al. 2001a).
Category: