How does a scroll pane do scrolling

In windows, Java, etc, the scroll pane scrolls t开发者_如何学运维he widgets inside. What I'm wondering is, how exactly does it do its scrolling? Does it change the location of each nested widget, or does it have a content widget that it moves around? Or is it something else? Also, when both scrollbars are present, how does it mask that little square at the bottom right? That square is sometimes used to resize. Is it a separate nested widget?

Thanks

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I think it just changes the location of the widget, button, or thing-a-ma-bober.

But my second guess would be it just draws the components "outside" of the scroll pane without being seen and when you scroll it just redraws dynamically.