一个“>”导致我调试了1个小时才解决问题

在XAML里面写了如下的代码：

    <DataTemplate x:Key="DT_HintCategory">
      <Expander HorizontalContentAlignment="Stretch"
                      ExpandDirection="Down"
                      Expanded="Expander_Expanded"
                      Header="AAA"
                      IsExpanded="{Binding Path=IsExpanded,
                                           Mode=TwoWay}">
        <Expander.Content>
          <ListBox x:Name="PART_HINTS" IsSynchronizedWithCurrentItem="False">>
            <ListBox.ItemsSource>
              <PriorityBinding>
                <Binding Path="HintsSlow" IsAsync="True" />
                <Binding Path="HintsFast" IsAsync="False" />
              </PriorityBinding>
            </ListBox.ItemsSource>
            <ListBox.ItemTemplate>
              <DataTemplate>
                <StackPanel>
                  <TextBlock Text="{Binding Name}" />
                </StackPanel>
              </DataTemplate>
            </ListBox.ItemTemplate>
          </ListBox>
        </Expander.Content>
      </Expander>
    </DataTemplate>

原因就是： <ListBox x:Name="PART_HINTS" IsSynchronizedWithCurrentItem="False">>（多写了一个大于号！）

结果在设计界面显示：An Unhandled Exception has occured: Click here to reload the designer.

在调试过程中，报： 

{"Add value to collection of type 'System.Windows.Controls.ItemCollection' threw an exception."}

Inner Exception:　{"Operation is not valid while ItemsSource is in use. Access and modify elements with ItemsControl.ItemsSource instead."}