Provide alternative content to ``++<object>++`` elements.

[source,html,diff-id=1,diff-type=compliant]
----
<object>This application shows the simulation of two particles colliding</object>

<object>
  <img src="flower.png" alt="Flower growing in a pot" />
</object>

<object>
  <object>
    This application shows the simulation of two particles colliding
  </object>
</object>
----
