42In the light of the foregoing, the answer to the fourth question is that, in circumstances such as those in the main proceedings, Article 4(1) of Regulation No 44/2001 must be interpreted as meaning that it does not preclude the application of Article 5(3) of that regulation to an action for liability arising from the operation of an internet site against a defendant who is probably a European Union citizen but whose whereabouts are unknown if the court seised of the case does not have firm evidence to support the conclusion that the defendant is in fact domiciled outside the European Union.