This example demonstrates how D3 margins define the inner plotting area within an SVG canvas. It renders a single gray rectangle positioned at the top-left margin boundary, with its width and height calculated by subtracting the margin values from the total container dimensions. The visualization uses D3’s selection join operator to create and update the SVG and rectangle elements, leveraging the `select`, `selectAll`, and `join` APIs. The container’s client width and height determine the overall canvas size.