Constant xcb::xproto::CW_BACKING_PIXEL

pub const CW_BACKING_PIXEL: Cw = 0x100;

The backing-pixel specifies what value to use in planes not covered by backing-planes. The server is free to save only the specified bit planes in the backing-store or save-under and regenerate the remaining planes with the specified pixel value. Any bits beyond the specified depth of the window in these values are simply ignored.