Is it possible to mix and PriorityBinding MultiBinding in WPF?

<TextBlock>
 
<TextBlock.Text>
   
<PriorityBinding TargetNullValue="{x:Static sys:String.Empty}">
      <Binding Path="Client.Address.PoBox" />
      <MultiBinding
StringFormat="{}{0} {1}">
        <Binding
Path="Client.Address.Street.Name" />
        <Binding
Path="Client.Address.Street.Number" />     
</MultiBinding>   
</PriorityBinding>
 
</TextBlock.Text>
</TextBlock>