This example demonstrates how SVG masks can create a striking visual composition using only rectangles and circles. It renders 100 horizontal and 100 vertical thin rect elements across the full viewport, with each set masked by a circular aperture defined via native SVG `mask` elements. The first mask uses a white circle on a black background, while the second inverts the colors to alternate visibility between the two rectangle sets. No D3 library calls appear in the code; instead, it relies on `document.createElementNS` and `setAttribute` for all SVG construction, making it a pure vanilla JavaScript and SVG demonstration.