yet another sizePolicy prob: how can I get a QTextBrowser to scale with its QTabWidg

[plipson]

My mainWindow has a centralWidget with a QTabWidget filling it; I want one of the tab pages to have a stretchable widget filling it as well. I haven't been able to get it to work with QT designer, even when I hand-edit the XML file to ensure I have the structure I want.
It seems that the solution should be to set the SizePolicy property correctly, but even though I've put either "Ignored" or "Expanding" on each QWidget, and tried setting the horstretch attributes, it won't stretch. I'm using CTRL-R within QTDesigner to check it.
I see other posts similar to this, but none seem to have any answer. I'm attaching a tiny demo UI file, too.