什么是String.Format的WPF XAML数据绑定等价物？

<TextBlock>
    <TextBlock.Text>
       <MultiBinding Converter="{StaticResource StringFormatConverter}">
           <Binding Path="FirstName" />
           <Binding Path="LastName" />
        </MultiBinding>
    </TextBlock.Text>
</TextBlock>

public class StringFormatConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
    {
        if (values == null || values.Length == 0 || string.IsNullOrEmpty(parameter as string))
        {
            return string.Empty;
        }

        return string.Format(parameter as string, values);
    }

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