“Domestic” law is explicitly distinguished from treaty law.

According to plaintiffs, "the [Internal Revenue] Code need not expressly provide for a foreign tax credit if the foreign levy in question falls within the treaty definition of a creditable tax" because "what constitutes a United States income tax for purposes of the application of a treaty derives from the treaty's definition and not from domestic law."32 (emphasis in original; alteration added). Plaintiffs argue that "[d]omestic law therefore does not constitute an absolute limitation on the rights and entitlements that may be granted to treaty beneficiaries under the terms of a U.S. tax treaty." (alteration added). Plaintiffs state that "[t]he parties agree that the NIIT constitutes a United States income tax as defined in Article 2(1) and 2(2) of the French Treaty," and, therefore, "that when a treaty provides a definition of a covered tax, it is that definition, and not the more limited definition under United States or foreign law, that is applied." (alteration added).