This example reproduces a Sol LeWitt art piece using D3 v6. It creates a grid of horizontal and vertical rectangles that are selectively revealed through two SVG masks. The masks use D3’s `symbol` and `symbols` APIs to generate geometric shapes, which act as windows showing either the horizontal or vertical lines. Rectangles are generated with `range`, `selectAll`, and `join`, while `renderMask` is called via `svg.call` to apply the two mask layers.