This example demonstrates animated, data-driven updates of SVG circles using D3’s selection API. A set of circles oscillates vertically and horizontally, with their count varying sinusoidally over time. The code uses `d3.select`, `d3.range`, and the classic pre-v6 `selectAll`, `enter`, `merge`, and `exit` methods to manage additions, updates, and removals, running on a 60 FPS timer. It relies on D3 v6.6.1, rendering SVG with real-time animation.