Here's some content at the top of the page

Drag the double arrow in the bottom-right to resize the SWF.

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And here is the bottom content. The final result feels a little buggy because you have to keep the mouse over the SWF all the time while dragging, which means you can't move the mouse as fast as you'd assume. This is not a problem in practical usage because you would generally have a toggle button which switches the SWF between two set sizes, or do something clever in JS to deal with situations where the mouse goes outside the SWF.