And as long as you can have tabs on any side of a window, how about multiple tabs on the same window? Like child tabs as well as label tabs, that are links to other windows.
Another cool use of vertical tabs is for the tabs on the left to select between windows, and the tabs on the right select between children of the current window (not sub-windows, but related windows or sub-directories). And you can use the tabs along the top as breadcrumbs to navigate back up the tree.
Some IDEs kind of do that with a directory browser on the left and a function browser on the right, but with outlines and scrolling lists instead of actual tabs.
You could navigate the tab tree by clicking or gesturing left or right with a pie menu on a tab, sliding the right column of tabs over to the left to descend into the tree.
Like a Finder window that shows directories as tabs on the right instead of icons inside.
You could also have top and bottom edge tabs for different kinds of children (i.e. xml attributes vs elements, object methods vs properties, different views or editors, etc).
The original NeXT file browser had breadcrumbs along the top (but not tabs):
Another cool use of vertical tabs is for the tabs on the left to select between windows, and the tabs on the right select between children of the current window (not sub-windows, but related windows or sub-directories). And you can use the tabs along the top as breadcrumbs to navigate back up the tree.
Some IDEs kind of do that with a directory browser on the left and a function browser on the right, but with outlines and scrolling lists instead of actual tabs.
You could navigate the tab tree by clicking or gesturing left or right with a pie menu on a tab, sliding the right column of tabs over to the left to descend into the tree.
Like a Finder window that shows directories as tabs on the right instead of icons inside.
You could also have top and bottom edge tabs for different kinds of children (i.e. xml attributes vs elements, object methods vs properties, different views or editors, etc).
The original NeXT file browser had breadcrumbs along the top (but not tabs):
https://www.youtube.com/watch?v=rrTag7nSHlw&t=701s