Questions of foreign state immunity frequently involve the ‘liminal space’ between substance and procedure, between domestic and international law and between the domestic law of the forum states and domestic laws of other states. US courts typically (and rightly) rest their analysis not only upon relevant foreign law and international practice but also upon procedural norms that are not formally part of the Foreign Sovereign Immunities Act. Immunity frequently implicates both the reach and power of domestic courts and the authority, organization and expectations of foreign states. It is unsurprising, therefore, that the domestic procedures of the forum court and the internal laws of both the forum state and the foreign state play significant roles in immunity determinations, although the relative paucity of concrete evidence of state practice can make it very difficult to discern the content of customary international law. ‘Restatements of domestic law’ can play an important role in developing principles of immunity, perhaps especially in the liminal spaces between domestic and foreign, substance and procedure. Hopefully, institutes in other countries will produce works like the Restatement of the Law (Fourth): The Foreign Relations Law of the United States.

中文翻译：

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作为阈限空间的主权豁免

外国豁免问题经常涉及实质与程序之间、国内法与国际法之间、法院地国国内法与他国国内法之间的“极限空间”。美国法院通常（并且正确地）不仅根据相关的外国法律和国际惯例进行分析，而且还根据不属于《外国主权豁免法》正式一部分的程序规范进行分析。豁免权经常涉及国内法院的范围和权力以及外国的权威、组织和期望。因此，法院地的国内程序以及法院地国和外国的国内法在豁免决定中发挥重要作用也就不足为奇了，尽管国家实践的具体证据相对缺乏，因此很难辨别习惯国际法的内容。“重述国内法”可以在制定豁免原则方面发挥重要作用，尤其是在国内和国外、实质和程序之间的界限空间中。希望其他国家的研究机构能够制作出像《法律重述（第四）：美国对外关系法》这样的作品。