DateTimeInterface is not a usable interface?

Hello, I was looking at DateTimeInterface in order to provide my own implementation of it, when I hit this: http://3v4l.org/8GvgO > "Fatal error: DateTimeInterface can't be implemented by user classes in" Is there any actual reason for this kind of limitation? Can it be removed before going stable? I also wasn't able to find any RFC information around it on https://wiki.php.net/rfc#php_55 - is there any previous discussion around this, or did it just sneak its way in? Greets, Marco Pivetta http://twitter.com/Ocramius http://ocramius.github.com/