As EU law currently stands – most notably with the binding Charter – it must be assumed, in line with established case-law, that these elements are satisfied in principle (cf. BVerfGE 73, 339 <387>; 102, 147 <162 et seq.>; 118, 79 <95 et seq.>; 129, 186 <199>; established case-law). In this respect, the fundamental rights of the Basic Law only serve as a backup guarantee. A constitutional complaint invoking this backup guarantee is subject to strict substantiation requirements (cf. BVerfGE 102, 147 <164>). 48 The other review options reserved by the Federal Constitutional Court, the review on the basis of the ultra vires doctrine (ultra vires review) and the review on the basis of constitutional identity (identity review) (cf. BVerfGE 123, 267 <353 and 354>; 126, 286 <302 et seq.>; 134, 366 <382 et seq. para. 22 et seq.>; 140, 317 <336 and 337 paras. 42 and 43>; 142, 123 <194 et seq. para. 136 et seq.>; 146, 216 <252 et seq. para. 52 et seq.>; BVerfG, Judgment of the Second Senate of 30 July 2019 - 2 BvR 1685/14 inter alia -, para. 120 et seq.), are not engaged by the proceedings at hand. 49 6. To the extent that the fundamental rights of the Basic Law are inapplicable due to the precedence of EU law, the Federal Constitutional Court reviews the domestic application of EU law by German authorities on the basis of EU fundamental rights (regarding constitutional court review on the basis of the Charter, cf. Constitutional Court of Austria, Judgment of 14 March 2012, U 466/11 inter alia, AT:VFGH:2012:U466.2011, sub. 5.5; cf. also Constitutional Court of Belgium, Judgment of 15 March 2018, No. 29/2018, B.9., B.10.5., B.15. et seq.; Conseil constitutionnel, Judgment of 26 July 2018, no. 2018-768 DC, paras. 10, 12, 38; Corte costituzionale, Decision of 23 January 2019, no. 20/2019, IT:COST:2019:20, paras. 2.1, 2.3). 50 c) In its past decisions, the Federal Constitutional Court has not yet expressly considered the possibility of directly conducting a review on the basis of EU fundamental rights. In cases where the fundamental rights of the Basic Law were found to be inapplicable due to the precedence of EU law, the Federal Constitutional Court has so far completely refrained from conducting a review of the asserted fundamental rights violations and instead left the review of whether fundamental rights were respected in the relevant case to the ordinary courts in cooperation with the Court of Justice of the European Union. Those decisions of the Federal Constitutional Court directly or indirectly concerned challenges to the validity of EU law. In those cases, the Federal Constitutional Court had to decide whether it can review the validity of certain EU decisions (cf., e.g., BVerfGE 129, 186 <198 and 199> – Investment Subsidies Act –), provisions of EU law (cf., e.g., BVerfGE 73, 339 <374 et seq.> – Solange II –; 102, 147 <160 et seq.> – The Common Organisation of the Market in Bananas –), or German legal provisions for the domestic implementation of binding EU law (cf., e.g., BVerfGE 118, 79 <95 and 96> with further references). Given that it is only for the Court of Justice of the European Union to annul EU law or declare it void, the Federal Constitutional Court has completely refrained from conducting a review on the basis of fundamental rights in such cases. There is no need to decide whether and to what 51 10/36