How to declare a string resource that bound to a property?

As you may know, we can declare a string "variable" using开发者_Go百科 resource:

<sys:String x:Key="someKey">someValue</sys:String>

I want to replace someValue by a binding property, how can I do it?

I don't think its possible. But even then, why do you need to do this. Couldn't your controls just bind to the same string instead of using the resource?