A Tinderbox document window will always contain a minimum of one tab. By default new blank windows open with two tabs. The second tab may then be closed or additional tabs opened as required.
Beneath the tab bar the window is split into 2 halves by a (moveable) splitter bar. The left side forms the 'View pane', holding a main view such as a Map or Outline, and that equate to a major view type window in pre-v6 Tinderbox.
The right side of the window is used for the 'Text pane' and which equates to a text window in pre-v6 Tinderbox.