WPF Validation and MVVM

Hello,

I have a View which has custom validation rules applied to some TextBoxes.

My problem is my View has a Save Button bound to a Command, which has a CanSave boolean method for being enabled.

The ViewModel has no knowledge of my View's Validation success or failures, so the button is enabled always. My validation logic is not in my ViewModel or Model, because I'm using custom validation rules, my View simply has the validation bindings directly in it (just like it should be).

So my question is, how on earth can someone check the validation rules (at least if any exist) within a ViewModel when the View is the one that has the bindings to custom validation rules?