Converter is a Markup

If you want simplify your code it’s better to make a converter who is also a markup

Previous code for converter

public class BoolToVisivilityConverter : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return (bool)value ? Visibility.Visible : Visibility.Collapsed;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

Previous code for xaml

<Grid  Margin="10,245,0,0"
               HorizontalAlignment="Left"
               VerticalAlignment="Top">
            <Grid.Resources>
                <local:BoolToVisivilityConverter x:Key="btvc" />
            </Grid.Resources>
            <TextBox Width="772"
                     Height="52"
                     Text="{Binding Dossier, FallbackValue=xxxxx}"
                     TextWrapping="Wrap"
                     Visibility="{Binding IsVisible, Converter={StaticResource btvc}}" />
        </Grid>

And new code for converter

 public class BoolToVisivilityMarkupConverter : MarkupExtension, IValueConverter
    {
        public override object ProvideValue(IServiceProvider serviceProvider) => this;

        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return (bool)value ? Visibility.Visible : Visibility.Collapsed;
        }

        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }

and xaml 

 <TextBox HorizontalAlignment="Left"
                 Height="38"
                 Margin="10,320,0,0"
                 TextWrapping="Wrap"
                 Text="{Binding Dossier, FallbackValue=xxxxx}"
                 VerticalAlignment="Top"
                 Width="772"
                 Visibility="{Binding IsVisible, Converter={local:BoolToVisivilityMarkupConverter}}" />

see the difference