Safari sees through filename extension lies

Here is the main text of a bug report I filed this morning with Apple:

If I use Photoshop to save a PSD file, and then rename that file so that its filename extension indicates it's a GIF file, I've just created a bogus file which most applications will not be able to figure out. Firefox and Internet Explorer display empty boxes. Photoshop itself cannot open such a file, even though internally the file is in Photoshop's native format.

Unlike most applications, Safari figures out that the filename extension is a lie and displays the image correctly. Ordinarily, I would pat Safari on the back for being better than everybody else. However, in this case, it can cause confusion.

Suppose you're learning web publishing and you make the mistake of thinking you can change a filename extension and the file will be magically translated into the corresponding format. This is a pretty common mistake among learners. If you are authoring a site with Safari as your test engine, you can "get away with" this mistake. However, when you test with other browsers, you discover your images don't work. You get empty boxes.

Here's why this is a particularly toxic situation: Part of learning web publishing is learning HTML. While you're learning, you make lots of HTML mistakes, and HTML mistakes resulting in empty boxes instead of images are quite common. When you see the empty boxes caused by the filename extension mistake, you assume there's a problem in your HTML, and you stare at it for hours, scratching your head, getting nowhere, because your HTML is perfect.

So, as annoying as it may seem, I am asking you to make Safari stupider. Please make it stop seeing through filename extension lies. No other app does it, and nobody makes Safari-specific sites, so there's no upside, and the downside is that it confuses people who are trying to learn web publishing.