Could someone explain me why when exactly one is written windows property of workbook in the code below.

I found in a book this listing, its aim is to count all visible workbooks and i do not understand why one is written in brackets.
Thank you in advance.

```
Public Function lCountVisibleWorkbooks() As Long

    Dim lCount As Long
    Dim wkbBook As Workbook
    For Each wkbBook In Application.Workbooks
        If wkbBook.Windows(1).Visible Then
            lCount = lCount + 1
        End If
    Next wkbBook
    lCountVisibleWorkbooks = lCount
End Function

```