This example uses D3 to draw a square outline with a set of lines and circles within it, arranged to explore the marks-and-channels concept of shape. The code leverages D3’s SVG manipulators—appending a `<rect>`, `<line>`s, and `<circle>`s via `select`, `append`, and `attr`—with fixed coordinates to create a geometric composition. Rendered as SVG on a white background, the square’s stroke and fill, the gray lines, and the dark circles demonstrate varied visual channels.