left-fringe-width

left-fringe-width is a variable defined in `C source code'.
Its value is

nil

• Automatically becomes buffer-local when set.

Documentation:
Width of this buffer's left fringe (in pixels).
A value of 0 means no left fringe is shown in this buffer's window.
A value of nil means to use the left fringe width from the window's frame.

Setting this variable does not take effect until a new buffer is displayed
in a window. To make the change take effect, call `set-window-buffer'.