This example visualizes the Iris dataset as an animated scatter plot, with dropdown menus to switch which numeric columns are mapped to the X and Y axes. It uses D3 v6 features such as `selection.join`, `scaleLinear`, `axisLeft`, `axisBottom`, and `transition` with a one-second duration to smoothly move circles and axes when selections change. New points grow from radius zero via a transition, while updating points reposition with a staggered delay. The SVG rendering fills the window, and menus are built with a reusable `menu` module dispatching change events.