A simple D3.js example demonstrates a basic tooltip for a single SVG circle. The visualization shows a 300-by-300 pixel canvas with one aliceblue circle at its center. Hovering over the circle reveals a text label that follows the mouse cursor, positioning itself near the pointer using the element's `mousemove` event. The tooltip is implemented with a div element whose visibility is toggled by `mouseover` and `mouseout` handlers, and its position updates via `event.pageX` and `event.pageY`. The code uses D3's selection and event-handling APIs to attach these interactions to the circle. This example illustrates the basic pattern for adding interactive hover information to a simple geometric shape.