DoAndIfThenElse

Hi, I recently found a mention of DoAndIfThenElse extension somewhere. I looked inside the ghc user guide and could not find any such extension. Then I looked in the ghc man page, no mention. I googled and found a very sparse references to it here and there. Then I tried using the extension with ghc and ghc seems to accept it. What's the story behind this, why is it not documented but accepted? thanks, harendra