This example creates a full-screen SVG image built entirely from programmatically generated rectangles. It demonstrates two different mask patterns that reveal a central circular area, with one mask applied to horizontal bars and another to vertical bars. The code uses D3.js version 6.6.1, specifically the `selection` module, alongside vanilla JavaScript DOM manipulation with `document.createElementNS` and SVG attributes. The rendering approach shows raw SVG element creation without using D3's data join or helper functions.