<!DOCTYPE html>
<html>
<body>
<figure>
  <figcaption>External Caption</figcaption>
  <figure>
    <img src="greenbox.png" alt="This is a green box.">
    <figcaption>Internal caption</figcaption>
  </figure>
</figure>
<figure>
  <figure>
    <img src="greenbox.png" alt="This is a green box.">
    <figcaption>Internal caption</figcaption>
  </figure>
  <figcaption>External Caption</figcaption>
</figure>
</body>
</html>