This is available only in Ted4 and Fred4, and not in the GN4 browser.
You can drag items from the current content tab to another main tab, as long both tabs are currently open.
Example
You selected two images on the Shell main tab, and you want to drop them in an article that is opened on the Articles main tab.
1.Start dragging the selection over the target main tab (in this example, Articles).
2.Wait 1 second, until the Articles main tab comes in the foreground.
3.Drop the images on the article tree.
See also
Using clipboard for cross-tab content managing