QML nested namespaces can't be used to define a property type

import QtQuick 2.4 as QQ

QQ.Rectangle {
  property QQ.Rectangle fooobar

  width: 100
  height: 100
  color: "yellow"
}

I'm using a nested namespace for importing a component, so I was guessing that I could use a type defined there also as a property type... But it's not possible while I'm getting this output

file:///tmp/qq.qml:4 Unexpected token `.'
file:///tmp/qq.qml:4 Expected token `:'