Variable: display-line-numbers-offset
display-line-numbers-offset is a buffer-local variable defined in
xdisp.c.
Documentation
A signed integer added to each absolute line number.
When this variable is non-zero, line numbers are always counted from
the beginning of the buffer even if display-line-numbers-widen is nil.
It has no effect when set to 0, or when line numbers are not absolute.
Probably introduced at or before Emacs version 27.1.
Source Code
// Defined in /usr/src/emacs/src/xdisp.c
DEFVAR_INT ("display-line-numbers-offset", display_line_numbers_offset,
doc: /* A signed integer added to each absolute line number.
When this variable is non-zero, line numbers are always counted from
the beginning of the buffer even if `display-line-numbers-widen' is nil.
It has no effect when set to 0, or when line numbers are not absolute. */);