In the PSE 15, grouping helps users to sort out a complex layer structure (fig. 1). Moreover, the groups can serve as limiters for knockout or adjustment effect.
If you open such a file in an older version of PSE, in the Layers palette you can see only the "closed folders" (fig. 2). You can neither browse the folders nor edit the nested items. Fortunately, the E+ easily solves the problem.
In the left panel of the "Layers" dialog, the groups can be recognized by the "node" symbol. After the group name [in the square brackets] you can read the number of nested items (fig. 3).
To look under the hood, you select the group in the list and apply the "Open Layer Group" command. Or simply double-click the group name in the Layers list.