Five circles animate across an SVG canvas, moving horizontally to new random positions before bouncing to new random sizes. The example demonstrates chained transitions in D3 v7, where the `d3.select` API chains multiple `.transition()` calls to sequence the position change over the first transition, followed by a second 750-millisecond transition with a `d3.easeBounce` easing function for the radius change. The update button triggers `updateAll()`, which regenerates random data for the `cx` and `r` attributes and re-applies the chained animation sequence.