I think the nested arrangement would work well for me, not least to limit the length of the object browser in some models.

As an example, I'm currently building a model of two townhouses. I have a sash window modelled in five separate parts (frame, top sash, ironmongery, etc) and imported from a separate component library. This is duplicated 20+ times in the scene at various preset widths, therefore if I need to select a specific part using the browser I then have to deselect several similar pieces scattered around the scene. A nested structure would allow me to select only the groups under an individual window reference (if I rename the top-level object after each import) - five linked parts with one click, or just a particular part of a particular window.

Having said that, it would also be useful to have a text-based filter facility so that the browser would show only windows, door handles or whatever. I imagine that this would be considerably more work, but it would mean that I could select, say, all glass items that may otherwise be hidden within windows, doors, rooflight and fixtures folders.

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A second point: Could a nested structure allow locking of objects within groups, relative to the group itself? What I mean to say is, could you lock the relationship of the components of a group to one another (so that the glass will always remain embedded in the frame, however I may accidentally click on it), but the window itself could be repositioned?