This example demonstrates the simplest possible D3 version 7 program: it selects the document’s `<body>` element and replaces its content with the text “Hello D3 version 7.” Rendered at a font size of 13 em, the message fills the screen. The code uses the `d3.select` API to query the DOM and the text method to set the content, with a single `index.js` file plus an HTML shell.