This example demonstrates two reusable legend components for D3 visualizations: a color legend mapping ordinal categories (apple, lemon, lime, orange) to distinct hues, and a size legend using a square-root scale to represent numeric values. The color legend renders colored circles with labels, while the size legend positions circles of varying radii with tick marks. Both use SVG groups and the `selection.merge` pattern for enter-update-exit handling, with styling applied via the `.tick` class.