Q: Bind custom control property with ListBox.Items My custom control has the following basic structure:
public class NewTextBox : TextBox
{
    public ItemCollection Items { get; set; }
}

And in XAML I have:
<ListBox Name="listBox1" />
<my:NewTextBox Items="{Binding Path=listBox1.Items}" />

The bind doesn't work in this case. Is the property Items wrong?

A: Your binding is incorrectly. Use the ElementName property in your binding to tell WPF where to look for the data, then bind to the Items property
<my:NewTextBox Items="{Binding ElementName=listBox1, Path=Items}" />

