How do you put a window back as a tab in IE9 once you've undocked it?

Question

I occasionally accidentally undock a tab from IE9 so it's in its own window (no idea what I'm doing to do this).

How do I get the window back as a tab in my main IE window?

Answer 1

Drag the undocked tab (by the tab, not the window's title bar) so that the window disappears. Move the tab between two tabs on another IE9 window and drop it.