This example uses D3 v6 to render a full-screen SVG with 100 horizontal rectangles stacked vertically. A single white 150×150 pixel mask is applied via the `mask` API, revealing only the section of the striped pattern that overlaps the mask’s area. The code builds the visualization by appending a `<mask>` element, adding a white rectangle to it, and then joining data from `range(n)` to create the stripes. The CSS classes `.first` and `.second` are defined but unused, and the commented-out code suggests previous experiments with clip paths.