add non-equation example

[pkra]

The walker is (ultimately) fairly generic: it exposes an aria-owns trees with deeply nested aria-labels (not just leafs). The hard part is SRE's work for annotations and MathJax's work for visual representation which can easily be done for other content by other tools.

To get this point across, it might help to add a non-equation example, e.g., an SVG graphic or a complex CSS grid structure.