Admittedly, I was not at my most alert when I almost deleted a top-level folder containing other folders, 303 items altogether, in DN, but I think an anomaly in the selection process was also to blame.
I was deleting an item I’d just transferred to DTPro; a message box came up and I unthinkingly hit OK; as my finger rose from pressing the key the text of the message made it to my brain: “Do you really want to delete this folder of 303 items? There is no undo.” Horrors, no! Happily the old Command-period worked to bring up a cancel dialog and I think only 3 items were lost.
Then I looked to see how this happened. The item still open for reading (the thing I’d wanted to delete, call it Document A) was selected, all right; but also selected was a folder (Folder 1) that was completely unrelated. Document A was not inside Folder 1—how could they both be selected? I had done a search and was working my way through the search hits, reading, sorting, deleting. But in a previous stage of my work I had selected Folder 1. After the search somehow it stayed selected and when I hit delete, confident that it applied to the document open in the text pane and selected in the search results pane, the program chose to delete Folder 1 instead. I submit that this is not expected behavior, and–even with daily backups–consequences could be serious.
The view I was using, in case it matters, had the Folders list (TOC) down the left side, search results across the top, and text of the selected document in the lower right pane. The version of DN is the latest, 1.9.