Is there a way to manually / dynamically add errors to the Validation.Errors collection?
from http://www.wpftutorial.net/ValidationErrorByCode.html
ValidationError validationError = new ValidationError(regexValidationRule, textBox.GetBindingExpression(TextBox.TextProperty)); validationError.ErrorContent = "This is not a valid e-mail address"; Validation.MarkInvalid( textBox.GetBindingExpression(TextBox.TextProperty), validationError);