How to make WPF AutoCompleteBox accept more than one Propert

Question

I want to search in multiple fields in AutoCompleteBox, I want to search in ClientName if the user starts typing characters, and search in ClientNumber if the user starts typing numbers.

 

I searched on the internet and from this Answer I understand that I should use Converter to accomplish what I want, But unfortunately, they do not explain how can I write the converter!

<toolkit:AutoCompleteBox x:Name="txbClientName" FilterMode="StartsWith" IsTextCompletionEnabled="True" ItemsSource="{Binding ocClients}" ValueMemberBinding="{Binding Converter= {StaticResource ClientSearch}}" SelectedItem="{Binding ElementName=this, Path=ContactPerson, Mode=TwoWay, UpdateSourceTrigger=LostFocus}" PreviewKeyUp="txbClientName_PreviewKeyUp" LostFocus="txbClientName_LostFocus">
<toolkit:AutoCompleteBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal">
<Label Content="{Binding ContactPerson}"/></StackPanel>
</DataTemplate>
</toolkit:AutoCompleteBox.ItemTemplate>

public class ClientSearchConverter : IValueConverter
{
public object Convert(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
//What should I write here !!!
}
public object ConvertBack(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
throw new System.NotImplementedException();
}
}

Any Help