Variable: scroll-bar-width
scroll-bar-width is a buffer-local variable defined in buffer.c.
Documentation
Width of this buffer's vertical scroll bars in pixels.
A value of nil means to use the scroll bar width from the window's frame.
Probably introduced at or before Emacs version 19.29.
Source Code
// Defined in /usr/src/emacs/src/buffer.c
DEFVAR_PER_BUFFER ("scroll-bar-width", &BVAR (current_buffer, scroll_bar_width),
Qintegerp,
doc: /* Width of this buffer's vertical scroll bars in pixels.
A value of nil means to use the scroll bar width from the window's frame. */);