Improve docstring of 'frame-scale-factor'

* src/frame.c (Fframe_scale_factor): Explain what happens when the
FRAME argument is nil.

diff --git a/src/frame.c b/src/frame.c
index bbdc3b55992e1eeab2f9e6e09d0be2802fd0f46f..028a45afeb73f6de1300bbe5bf8ae867064cd554 100644 (file)
--- a/src/frame.c
+++ b/src/frame.c
@@ -3747,6 +3747,7 @@ window state change flag is reset.  */)
 DEFUN ("frame-scale-factor", Fframe_scale_factor, Sframe_scale_factor,
        0, 1, 0,
        doc: /* Return FRAMEs scale factor.
+If FRAME is omitted or nil, the selected frame is used.
 The scale factor is the amount by which a logical pixel size must be
 multiplied to find the real number of pixels.  */)
      (Lisp_Object frame)