QT Designer adds QGridLayout in generated XML but not visible in Object Inspector

[clhallinan]

I have a .ui file which is part of a github project. (ie I didn't design it.)
QT Creator/Designer is instantiating a QGridLayout in the xml file, but that component is not visible in the form previewer nor the Object Inspector. Here is a snippet of code from my .ui form XML file:

...
 <layout class="QGridLayout" name="gridLayout">
 <property name=...>  (Several related properties not relevant)
      <item row="0" column="0">
            <widget class="qfi_NAV" name="graphicsNAV">
         ...
            <property xxx...> (lots of properties)
        ...
            </widget>
      </item>
  </layout>

However, the only three items shown in the form designer's Object Inspector are:

myWidget  |  QWidget
    myFrame  |  QFrame
        graphicsNAV  |  qfi_Nav   (my own subclass of QGraphicsView)

Any idea why I don't see the QGridLayout which gets autogenerated from this .ui form? Why doesn't it appear on Object Inspector in QT Design mode? Where is this QGridLayout coming from and how do I control its properties if I can't see it?

Thanks.