The meaning of pair1 and pair2 in the xml file

[Lamed-git]

Dear Tadano,
I want to extract the Hessian matrix from the alamode xml file, but I'm not sure what pair1 and pair2 mean in the HARMONIC part of the xml and how to extend them. My understanding is that pair1 = "iatom ixyz", pair2 = "jatom jxyz ?" I'm not quite sure what third data in pair2 means and whether my understanding is accurate. At the same time, iatom in pair1 should be the number of atoms in the primary cell, how can it be extended to the supercell?
Looking for your reply! Thank you very much.