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Vladimir Vukićević was attempting to find out why the performance of Firefox 3 builds was hitting a plateau, when he noticed that Safari was happily drawing pages at twice the frame rate.

Digging around in Apple's WebKit engine, which drives Safari, he spotted over 100 undocumented "OS-secrets-only-WebKit-knows".

"Reading the WebKit code is pretty interesting; there are all sorts of potentially useful Cocoa internals bits you can pick up...," he says. "Would any other apps like to take advantage of some of that functionality? I'm pretty sure the answer there is yes, but they can't."

Vukićević is clear that he does not think Apple is being malicious by purposely trying to cripple third party software, as the hyperbolic

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Slashdot poster had claimed. Only that "the undocumented functionality could be useful for Firefox and other apps to implement things in an simpler (and potentially more efficient) manner."

And he adds that Firefox 3 will show that the APIs do not guarantee Safari has an advantage.

Responding to Vukićević's blog post, WebKit developer David Hyatt says that it would have been dangerous to make the APIs public.

"We aren't really happy with that code in WebKit, but we had to do it to avoid performance regressions in apps that embedded WebKit," he says, without adding that WekBkit apps make quite a long list.

"Many of the private methods that WebKit uses are private for a reason," he says. "Either they expose internal structures that can't be depended on, or they are part of something inside a framework that may not be fully formed."

Hyatt adds that, as Vukićević notes himself, "there was a totally acceptable public way of doing what you needed to do."