Alternative text on generated content?

There is a generated-content-image before this text.

Before this text there is generated content, too. However, the URL points to this HTML-File, not to an image. Since Opera doesn't support this, it should ignore the resource.
The exact style is:
#test2:before{
 content: "alternative text";
 content: url(test10.html);
}
So, since url(test10.html) should be ignored, "alternative text" should be displayed instead. But what Opera does is to display [Image] :-(