Set Focus to Checkbox in ComboBox in order to get keyboard control
<p>I have a <code>ComboBox</code> which has <code>CheckBox</code>es as items:</p>

<pre><code>&lt;ComboBox ItemsSource="{Binding SomeCollectionProperty}"&gt;
    &lt;ComboBox.ItemTemplate&gt;
        &lt;DataTemplate&gt;
            &lt;StackPanel Orientation="Horizontal"&gt;
                &lt;CheckBox IsChecked="{Binding SomeBoolProperty}" Width="20" /&gt;
                &lt;TextBlock Text="{Binding Name}" Width="140" /&gt;
            &lt;/StackPanel&gt;
        &lt;/DataTemplate&gt;
    &lt;/ComboBox.ItemTemplate&gt;
&lt;/ComboBox&gt;
</code></pre>

<p>If the <code>ComboBox</code> gets keyboard focus, I can select an item with the up and down arrow keys. I can then switch focus to the <code>CheckBox</code> with <kbd>tab</kbd> and am able to switch the <code>CheckBox</code>'s <code>IsChecked</code> state by pressing <kbd>space</kbd>.<br>
I'm looking for a solution that allows me to do the same but without manually switching focus to the <code>CheckBox</code>. My desired behavior would be:  </p>

<ol>
<li>Choose item with arrow keys</li>
<li>Choose state with <kbd>space</kbd></li>
</ol>

<p>I tried to do it with <code>EventTrigger</code> and <code>InputBinding</code> and by fiddling around with the <code>Focusable</code> property but with no luck.<br>
I would prefer a solution in <code>xaml</code> but a code-behind solution would still be appreciated.</p>