This example demonstrates dynamic data binding in D3 by continuously updating a set of circles that roam across the screen. An interval-driven animation recalculates the number and positions of circles based on a sine wave, while `selectAll` with `enter`, `merge`, and `exit` handles the creation, update, and removal of SVG elements. The code uses D3 v7’s `select`, `range`, and explicit update pattern, rendering directly to an SVG canvas sized to the viewport.