SlotAttachment
An attachment to a host that has its own method for holding children, such as JScrollPane.setViewportView, instead of the usual Container.add.
The host names its ChildPlacement:
ChildPlacement.Slots - named regions that hold one child each.
ChildPlacement.OrderedSlots - a host that holds many children in order, such as the tabs of a
JTabbedPane.
The attachment belongs to the host: the container composable wrapping it hands each of its regions the attachment that installs a component there. A child reaches a region through org.jetbrains.compose.swing.modifier.layout.slot, which names the region it fills.