According to CSS 1, section 5.3.5 and CSS 2.1, section 14.2.1, when background-attachment is scroll, then an image should scroll within its containing block, not within the viewport.
Instructions: resize vertically the browser window to change the vertical dimension of the viewport.
Expected results: the lime squared + image should remain vertically in the middle of its containining block, which is the body which has a lime border. The lime squared + image should not scroll up and down.
Credit must go to Ian "Hixie" Hickson for his background test 9 test case