This example demonstrates basic DOM manipulation with D3.js v4, showing how to select and modify elements in an HTML document. It changes the text and styling of an existing heading, applies red coloring to it, and appends three new paragraph elements to the body. The code uses `d3.select` and `d3.selectAll` to target the heading and paragraphs, then chains `.style`, `.attr`, `.text`, and `.append` methods to update content and set colors. All paragraphs are colored blue, while the heading receives a red style and a new class attribute.