mozilla-release/testing/web-platform/tests/html-longdesc/external-image-with-relative-base-external-description-manual.html

<!DOCTYPE html>
<html>
 <head>
  <title>Longdesc test: External image, external description, relative base</title>
  <base href="./rebased/">
 </head>
 <body>
  <img src="picture2.png" alt="the image" longdesc="fail.html">
  <p>If the image is broken, the base element has not been interpreted correctly so the test result is unknowable</p>
 </body>
</html>