This example uses SVG masks to create an intersecting grid of horizontal and vertical lines, revealing a circular window at the center. The code employs `d3.select` and `d3.range` to generate two sets of 100 rectangles, one for each orientation, and applies a mask with a white circle over a black background to the horizontal lines, and a mask with a black circle over a white background to the vertical lines. The result is a cross-hatched pattern that becomes visible only inside the central circle.