WPF databinding & DependencyProperties

Question

I have got an userControl which contains a textblock and a textbox, but I am stuck trying to pass arguments to it via DependencyProperties.

here is some stuff:

the userControl XAML:

<UserControl x:Class="WpfApp1.Controls.InfoField"
             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:WpfApp1.Controls"
             mc:Ignorable="d" 
             DataContext="{Binding RelativeSource={RelativeSource Self}}"
             >
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto"></ColumnDefinition>
            <ColumnDefinition Width="Auto"></ColumnDefinition>

        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"></RowDefinition>

        </Grid.RowDefinitions>
        <DockPanel>
            <TextBlock Text="{Binding TextInBlock}" HorizontalAlignment="Right" Margin="2" Width="160"></TextBlock>
            <TextBox Text="{Binding BindingInBox}" Grid.Column="1" Width="200" Margin="2"></TextBox>
        </DockPanel>
    </Grid>
</UserControl>

the associated code behind:

using System.Windows;
using System.Windows.Controls;

namespace WpfApp1.Controls
{
    /// <summary>
    /// Logique d'interaction pour InfoField.xaml
    /// </summary>
    public partial class InfoField : UserControl
    {
        public static readonly DependencyProperty TextInBlockProperty =
            DependencyProperty.Register("TextInBlock", typeof(string), typeof(TextBlock));


        public static readonly DependencyProperty BindingInBoxProperty =
            DependencyProperty.Register("BindingInBox", typeof(string), typeof(TextBox));

        public string TextInBlock
        {
            get => (string) GetValue(TextInBlockProperty);
            set => SetValue(TextInBlockProperty, value);

        }

        public string BindingInBox
        {
            get => (string)GetValue(BindingInBoxProperty);
            set => SetValue(BindingInBoxProperty, value);

        }
        public InfoField()
        {
            InitializeComponent();
            this.DataContext = this;

        }
    }
}

and the MainWindow XAML:

 <Grid ColumnSpan="4" Row="1" Name="detailsGrid" 
              DataContext="{Binding ElementName=listBoxBooks,Path=SelectedItem}">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="Auto"></ColumnDefinition>
                <ColumnDefinition Width="Auto"></ColumnDefinition>
                <ColumnDefinition Width="Auto"></ColumnDefinition>
                <ColumnDefinition Width="Auto"></ColumnDefinition>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"></RowDefinition>
                <RowDefinition Height="Auto"></RowDefinition>
                <RowDefinition Height="Auto"></RowDefinition>
            </Grid.RowDefinitions>
------>     <controls:InfoField Grid.ColumnSpan="2" BindingInBox="{Binding Author,ElementName=mainWindow}" TextInBlock="Auteur :"></controls:InfoField> 
            <Button Grid.Row="0" Grid.Column="2" Click="ButtonBase_OnClick">Click me!</Button>

            <TextBlock Text="Titre :" HorizontalAlignment="Right" Grid.Row="1"></TextBlock>
            <TextBox Text="{Binding Title}" Grid.Column="1" Grid.Row="1" Width="200"></TextBox>

        </Grid>

at the time being, visual studio gives me an error, at the line at which I put a text arrow; the error says : "the 'TextInBlock' property is already registered by 'TextBlock'". I don't understand this error message. Please note that there is a difference between the 2 bindings, one references an other field (also via binding, the field being 'Author') whereas the other is just a simple string.

thank you.