String Resources for Xaml on a Win 7 Phone

I want to do something similar (but in win phone 7):

In Silverlight, I can use resources,

<sys:String x:Key="ResourceString">Resource String</sys:String>

And use it, for example:

<TextBlock Text="{StaticResource ResourceString}"></TextBlock>

The question arises:

How to use String resource in winphone 7?

Thank.