This example demonstrates a generative, full-browser visualization built with raw SVG elements and JavaScript. It constructs a grid of overlapping horizontal and vertical rectangles that is partially obscured by a circular mask, revealing only the central region of the layered pattern. The mask is defined with an SVG `<mask>` element and a white circle, while rectangles are created programmatically using the DOM API. The page also includes a separate React app that imports D3 to render a simple text message, showing integration between the two libraries.