This example renders a generative geometric composition using D3 v5, creating a grid of horizontal and vertical rectangles that are masked to reveal two contrasting overlays. The code builds an SVG canvas sized to the browser window, uses `d3.range` to generate 100 rectangles in each direction, and applies `d3.symbol` paths (including a triangle) as masks to selectively show or hide the grid lines. It demonstrates the use of `d3.select` for DOM manipulation and local module imports to organize code.