This example shows a simple SVG face created with D3.js, featuring a mouth drawn using the `arc()` API and a yellow rectangle appended inside a path via the custom `createArc` function. The face is centered in a 960×500 viewport using SVG transforms. It demonstrates basic D3 v5 selection and data-joining techniques, importing `select` and `arc` from the D3 library and rendering entirely in SVG markup.