This example renders a grid of alternating horizontal and vertical stripes across the full viewport, masked so that only a circular region in the center reveals the pattern while the rest stays black. It uses the SVG `mask` element and `circle` to define the visible area, dynamically creating `rect` elements with JavaScript to draw the stripes. The viewport dimensions are taken from `window.innerWidth` and `window.innerHeight`, and all drawing is done via the SVG namespace API.