The following xaml will crash if the converter is not registered:

<local:MultiIsLessThanConverter x:Key="NonEssentialsLayout"/>

<Style x:Key="NonEssentialsGrid" TargetType="Grid">

<Setter Property="Visibility" Value="Visible"/>

<Style.Triggers>

<DataTrigger Value="True">

<DataTrigger.Binding>

<MultiBinding Converter="{StaticResource NonEssentialsLayout}">

<Binding Path="ActualWidth" ElementName="NonEssentialsGrid"/>

<Binding Path="ActualWidth" ElementName="Exp_Name"/>

</MultiBinding>

</DataTrigger.Binding>

<Setter Property="Visibility" Value="Collapsed"/>

</DataTrigger>

</Style.Triggers>

</Style>