Open a popup - a borderless window that sits above this one and can hang outside it, the way an OS menu does. The position is in this window's client pixels, which is what a panel's <c>Box.Rect</c> is already in. <para> There is no size to pass. The popup is born hidden at the parent's size, shrinks to whatever is put in it, and only then appears - so what it ends up as is the size of its contents. </para>