Improve documentation of 'line-number-display-width'

* doc/lispref/display.texi (Size of Displayed Text): Document the
additional 2 columns used for line-number display.

* src/indent.c (Fline_number_display_width): Doc fix.  (Bug#28248)

2 files changed, 5 insertions, 3 deletions

diff --git a/doc/lispref/display.texi b/doc/lispref/display.texi
index afd09cfb330..fbdd810247d 100644
--- a/doc/lispref/display.texi
+++ b/doc/lispref/display.texi
@@ -2053,8 +2053,9 @@ This function returns the width used for displaying the line numbers
 in the selected window.  Optional argument @var{pixelwise}, if
 non-@code{nil}, means return the value in pixels; otherwise the value
 is returned in column units of the font defined for the
-@code{line-number} face.  If line numbers are not displayed in the
-selected window, the value is zero.  Use @code{with-selected-window}
+@code{line-number} face, and doesn't include the 2 columns used to pad
+the numbers.  If line numbers are not displayed in the selected
+window, the value is zero.  Use @code{with-selected-window}
 (@pxref{Selecting Windows}) if you need this information about another
 window.
 @end defun
diff --git a/src/indent.c b/src/indent.c
index be8676600a5..a3e9b5b0b9a 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -1993,7 +1993,8 @@ DEFUN ("line-number-display-width", Fline_number_display_width,
        doc: /* Return the width used for displaying line numbers in the selected window.
 If optional argument PIXELWISE is non-nil, return the width in pixels,
 otherwise return the width in columns of the face used to display
-line numbers, `line-number'.  */)
+line numbers, `line-number'.  Note that in the latter case, the value
+doesn't include the 2 columns used for padding the numbers.  */)
   (Lisp_Object pixelwise)
 {
   int width, pixel_width;