How can components be owned by other components in Projucer?

This may be documented somewhere but I have been unable to find it. Suppose I throw a bunch of buttons, labels, checkboxes, etc into a window component in Projucer.
Now suppose I insert a scrollbox (viewport?) component on to that window. How do I get all the buttons, labels, etc to now belong to that scrollbox? There doesn’t seem to be anything obvious where I can select a parent for a button, for example?

Do I have to do it all manually in code?

You are likely best off writing all your GUI code manually. The GUI designer in Projucer is basically deprecated at this point.

Really? That’s a shame.

The Projucer can only handle components with a static size and in a flat hierarchy, that’s why it makes sense to adopt new layout strategies like Grid and FlexBox or simply using Rectangle and removeFromTop() etc.

You can still create the inner components with the GUI editor and put these manually into the next layer.

However the GUI editor will get only bug fixes, no new features will be added, afaik.