# hdr_lines => string of various header lines for mode information
# mode_a => original mode of oid_a (string, not integer),
# ibx => PublicInbox::Inbox object containing the diff
# hdr_lines => string of various header lines for mode information
# mode_a => original mode of oid_a (string, not integer),
# ibx => PublicInbox::Inbox object containing the diff