如何绑定到ControlTemplate中的元素？

<ControlTemplate TargetType="local:CustomControl">
    <Grid>
        <Button Content="{TemplateBinding ButtonContent}" Command="{TemplateBinding ButtonCommand}" />
    </Grid>
</ControlTemplate>

[TemplatePart(Name = "PART_Button", Type = typeof(Button))]
public class CustomControl : Control
{
    static CustomControl()
    {
        DefaultStyleKeyProperty.OverrideMetadata(typeof(CustomControl), new FrameworkPropertyMetadata(typeof(CustomControl)));
    }

    public override void OnApplyTemplate()
    {
        base.OnApplyTemplate();

        Button button = GetTemplateChild("PART_Button") as Button;
        // 在这里可以对button进行操作和绑定其他属性
    }
}

<local:CustomControl ButtonContent="{Binding ButtonContent}" ButtonCommand="{Binding ButtonCommand}" />