WPF: in custom UserControl, expose its children's DependencyProperties.

MyUserControl.xaml

<UserControl
    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:my="clr-namespace:MyProject"
    x:Class="MyProject.MyUserControl"
    mc:Ignorable="d" d:DesignHeight="100" d:DesignWidth="640"
    >

    <Grid>

        <!--
            MyChildControl could be either a custom control or some built-in control.
            It has a read-write DependencyProperty named MyReadWriteProperty,
            and a readonly DependencyProperty named MyReadonlyProperty.
            Both of them can be accessed from property wrappers named MyReadWrite and MyReadonly.
        -->

        <my:MyChildControl x:Name="MyChild" />

    </Grid>

</UserControl>

MyUserControl.xaml.cs

public partial class MyUserControl : UserControl
{
    public MyUserControl()
    {
        InitializeComponent();
    }

    public string MyChildReadonly
    {
        get { return MyChild.MyReadonly; }
    }

    public string MyChildReadWrite
    {
        get { return MyChild.MyReadWrite; }
        set { MyChild.MyReadWrite = value; }
    }
}