You know you can grab any edge of a window and drag to resize the window. Everyone knows that. But… if you hold the Option key while you do it, the window grows in the opposite direction too! For example, if you’re grabbing a window’s right edge and dragging it to the right, the window grows to the right… unless you’re holding the Option key. In that case, the window also grows to the left! You have to try it to believe it. Works with up/down too. Try it!