ARTICLE 27
Modalities for Application
(1) The competent authorities of the Contracting States may jointly or separately resolve the mode of application of this Convention.
(2) In particular, for obtaining benefits under Articles 10, 11 and 12 in a Contracting State, residents of the other Contracting State shall, unless the competent authorities decide otherwise, submit a form of proof of residence indicating in particular the nature and the amount or value of income concerned including the certification of tax services of that other State.