[Ifeffit] How does AUTOBK handle the pre-edge background removal?

Dear Ifeffit list, There is one question I don't understand very well. How does AUTOBK algorithm handle the pre-edge background removal? I check the mannual of using ATHENA and the paper, "Near-edge x-ray-absorption fine strructure of Pb: A comparison of theory and experiment", M. Newville, et al., Phys. Rev., B47:21 (1993), 14126. Both of them have no information about dealing pre-edge background removal with AutoBK and how is it work within Athena? Hence, I ask this qustion for all the experts on the list. Thank you for your help. Sincerely, Yu-Chuan Lin Research Assistant Dept. of Chemical Engineering Kansas State University