Some sites have example code which is not completely viewable within the text field. But once there is an onClick or hover the code stretches out of the field or text box to show it all or allow it to be selected and copied. This effect does not move any of the existing layout. As if the reveal was on a different z-index.
I am sorry I do not have an example. If I stumble on it then I would probably not ask. I think I have seen it used in one of Chris examples too.