WPF，请问路由事件


<Grid Height="268" Name="grid1" Width="340" MouseUp="button1_MouseUp">
    <Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="82,97,0,0" Name="button1" VerticalAlignment="Top" Width="75" MouseUp="button1_MouseUp" />
</Grid>
Grid的MouseUp事件是冒泡事件，直接关联button1_MouseUp事件处理程序。但是下面的Click事件：<Grid Height="268" Name="grid1" Width="340" ButtonBase.Click="button1_Click">
   <Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="82,97,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click" />
</Grid>
为什么Grid的Click冒泡事件必须写成ButtonBase.Click，不写成Click事件呢？