This example creates a geometric grid pattern using D3 v6, rendering horizontal and vertical stripes across the full browser viewport. Two SVG masks reveal the stripes through circular windows in the center of the screen. The first mask shows vertical lines inside a white circle on a black background, while the second mask inverts this effect. The code uses D3’s `select`, `range`, and `join` methods to generate the rectangles, with SVG `mask` elements and `circle` shapes determining the visible regions.