title: WPF textbox that only updates binding when enter is pressed
body: <p>all.  I have a usercontrol "NumericTextBox" that only allows numeric entries.  I need to exhibit another specialized behaviour, that is, I need it to be able to bind it to a VM value OneWayToSource and only have the VM value update when I press enter while focusing the textbox.  I already have the an EnterPressed event that fires when I press the key, I'm just having a hard time figuring out a way to cause that action to update the binding...</p>