如何继承带占位符的WPF UserControl？

<UserControl x:Class="YourNamespace.CustomUserControl"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
             xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
             mc:Ignorable="d" 
             d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <ContentPresenter x:Name="ContentHolder" />
    </Grid>
</UserControl>

public partial class CustomUserControl : UserControl
{
    public static readonly DependencyProperty ContentProperty =
        DependencyProperty.Register("Content", typeof(object), typeof(CustomUserControl), new PropertyMetadata(null));

    public object Content
    {
        get { return GetValue(ContentProperty); }
        set { SetValue(ContentProperty, value); }
    }

    public CustomUserControl()
    {
        InitializeComponent();
        ContentHolder.DataContext = this;
    }
}

<local:CustomUserControl x:Class="YourNamespace.DerivedUserControl"
                         xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                         xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
                         xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
                         xmlns:local="clr-namespace:YourNamespace"
                         mc:Ignorable="d" 
                         d:DesignHeight="300" d:DesignWidth="300">
    <Grid>
        <!-- 添加具体的内容 -->
    </Grid>
</local:CustomUserControl>