`GtkGridLayout` is a layout manager which arranges child widgets in rows and columns.
Children have an "attach point" defined by the horizontal and vertical index of the cell they occupy; children can span multiple rows or
columns. The layout properties for setting the attach points and spans are set using the [[email protected]] associated to each
child widget.
The behaviour of `GtkGridLayout` when several children occupy the same grid cell is undefined.
`GtkGridLayout` can be used like a `GtkBoxLayout` if all children are attached to the same row or column; however, if you only ever need
a single row or column, you should consider using `GtkBoxLayout`.