ight, bottom or left. If
            omitted, the element occupies the entire cavity.

        sticky: nswe
            Specifies where the element is placed inside its
            allocated parcel.

        children: [sublayout... ]
            Specifies a list of elements to place inside the
            element. Each element is a tuple (or other sequence)
            where the first item is the layout name, and the other
            is a LAYOUT.Nr