A grid of alternating horizontal and vertical black-and-white rectangles becomes visible through two SVG masks, revealing a pattern of D3 symbol shapes rendered with `d3.symbol` and `d3.symbols`. The example uses `d3.select`, `d3.range`, and `d3.symbol` to generate the rectangles and mask paths, with the mask elements created programmatically and applied via the `mask` attribute. The output is a static SVG visualization, drawn across the full browser window, that demonstrates layered masking and the use of selection joins with `join`.