Shouldn't an item show in both the sub and parent group?

I’m confused about something… Let’s say I have a document, we’ll call it “a.pdf”. That file has been placed into a group called, “Group1”. When I click Group1, it shows a.pdf. Great!

Now, I want to further classify it. I create a new group called Group2. Group2 is a sub-group of Group1 (it’s indented below Group1, and Group1 has that little triangle view button which when clicked shows Group2).

I move a.pdf into Group2.

When I click Group2 (a subgroup of Group1) I see the document a.pdf.

When I click Group1, it shows nothing.

However, the little number to the right of both Group1 and Group2 BOTH say, “1” (indicating that there is a document inside that group).

This strikes me as odd behavior. I’d assume that clicking Group1 would show contents for Group1 and all sub-groups. Clicking the sub-groups would show the content of the sub-group and all child groups down from it.

But, what I get more closely resembles a file system of the computer. A folder contains other folders or documents. I can view the contents of a sub-folder by opening it. Folder 1 doesn’t show the contents of Folder 2, as one would expect.

Is this all be design, or is there something I’m just not understanding?

It is design. IMO, I suspect most users prefer the current behavior - like “the file system of a computer”, as @WolfSnap described it well. Also, IMO, DEVONthink is consistent with the way that most applications with a folder metaphor do things.

But - the other way is possible to. Merely go to three-pane view and select Group 1 and Group 2 at the same time, and you’ll see all the contents of both groups in the top-right pane. Like this: