How do I implement WPF group box than spans two columns?

Question

Here is the layout I want:

Grid with 2 columns, 2 rows

Row 1 should contain a group box that spans both columns. Row 2, Column 1 will contain a group box Row 2, Column 2 will contain another group box.

In row 1's group box, I want the left side to have a stack of labels/combo boxes. On the right side will be a stack of labels/checkboxes. In the Row 2/Column 1 group box, I want more labels/combo boxes that should align with the first row's labels/combo boxes. In the Row 2/Column 2 group box, I want more labels/checkboxes that align with the first row's labels/checkboxes.

Here is what I have so far. The problem I'm having is that the label/combo box pairs in row 1's group box want to span the entire group box. But, I am explicitly setting the row=0, column=0 for the inner grid that contains the labels/combo boxes.

Forgive me if this doesn't compile as I'm typing from a printout on a computer without Studio.

<Grid>
   <Grid.RowDefinitions>
      <RowDefinition/>
      <RowDefinition/>      
   </Grid.RowDefinitions>
   <Grid.ColumnDefinitions>
      <ColumnDefinition/>
      <ColumnDefinition/>
   <Grid.ColumnDefinitions>
   <GroupBox Grid.Row="0" Grid.Column="0" Grid.ColumnSpan="2">
      <GroupBox.Header>
         <Label Content="Device Configuration"></Label>
      </GroupBox.Header>
      <Grid Grid.Row="0" Column="0">
         <Grid.RowDefinitions>
            <RowDefinition/>
            <RowDefinition/>      
            <RowDefinition/>      
         </Grid.RowDefinitions>
         <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
         <Grid.ColumnDefinitions>

         <Label Grid.Column="0" Grid.Row="0" Content="Label 1"></Label>
         <ComboBox Grid.Column="1" Grid.Row="0"></ComboBox>

         <Label Grid.Column="0" Grid.Row="1" Content="Label 2"></Label>
         <ComboBox Grid.Column="1" Grid.Row="1"></ComboBox>

         <Label Grid.Column="0" Grid.Row="2" Content="Label 3"></Label>
         <ComboBox Grid.Column="1" Grid.Row="2"></ComboBox>
      </Grid>
   </GroupBox>
</Grid>

Answer 1

Once a control is no longer the direct descendant of a grid, it has no concept of being within the Grid panel, and isn't formatted as such. So, because there's a GroupBox in the way, it's not a direct descendant of the Grid.

If you want the contents of the GroupBox to look like they're part of the top-most Grid, you'll have to reproduce that Grid structure (2 columns in the GroupBox) on your own.

Visual Studio doesn't give any errors when you put Grid.* on items, even if the parent isn't a Grid.