OK, I've got this working nicely, including Todd's suggestion about keeping the mouse over the resize icon.
But it has one very important difference from the Frame use-case, in that normally a Sheet will not have preferredWidth and preferredHeight set, but clients will still want it to be resizable. If I permit that, then after the resizing operation, the Sheet object will have preferredWidth and preferredHeight explicitly set. I'm not sufficiently familiar with all the ins and outs to know if this is a problem?? -- Noel.
