Hello normal validation is always related to some control, but in my case there is no control to fire validation when its content changes and to show errortemplate to the user. because the data to be validated is in the cipboard. when the user presses "PASTE" button viewmodel processes the data and finds it to be invalid. but what is the best way to invoke WPF validation in this case? as far as i understand using IDataErrorInfo is the way to go, but what is the best way to start validation. and whst is the best way of displaying the error? errortemplate of the button element? Thanks a lot for help. Peter