The Catalogue's "New array component": what an array component IS, and the three ways to get one. An existing sheet can become one, because the usual way to find out you want an array is to have drawn one copy of it already.

What the Properties pane shows for the open sheet when it is an array component: nothing at all when it is not, so an ordinary sheet's properties are unchanged by the feature existing. The copy count is here rather than in a dialog because it is the sheet's most important property - it is what the sheet MEANS - and the pane is where a sheet's properties are.