According to Art. 123(2) EPC the European patent application or the European patent may not be amended in such a way that it contains subject-matter which extends beyond the content of the application as filed. The revision of the EPC has introduced a purely editorial change to the wording of Art. 123(2) EPC to bring it into line with Art. 123(1) EPC.
The concept of "content of the application as filed" relates to the parts of the European patent application which determine the disclosure of the invention, namely the description, the claims and the drawings (G 3/89, OJ 1993, 117, and G 11/91, OJ 1993, 125). See in this chapter at II.E.1.2. "Content of the application as filed: Parts of the application which determine the disclosure of the invention" below.
The underlying idea of Art. 123(2) EPC is that an applicant should not be allowed to improve his position by adding subject-matter not disclosed in the application as filed, which would give him an unwarranted advantage and could be damaging to the legal security of third parties relying on the content of the original application (see G 1/93, OJ 1994, 541). The public may not be confronted with an extent of protection, which could not have been established by a skilled person having studied the whole content of the technical disclosure of the originally filed patent application (T 157/90, see also T 187/91).
The "gold standard" (G 2/10, OJ 2012, 376) for assessing compliance with Art. 123(2) EPC is the following: any amendment to the parts of a European patent application or of a European patent relating to the disclosure (the description, claims and drawings) is subject to the mandatory prohibition on extension laid down in Art. 123(2) EPC and can therefore, irrespective of the context of the amendment made, only be made within the limits of what a skilled person would derive directly and unambiguously, using common general knowledge, and seen objectively and relative to the date of filing, from the whole of these documents as filed (G 3/89, OJ 1993, 117; G 11/91, OJ 1993, 125). After the amendment the skilled person may not be presented with new technical information (G 2/10; see however G 1/16 for undisclosed disclaimers). For details, see in this chapter II.E.1.3. "Standard for assessing compliance with Article 123(2) EPC" further below; for more details on G 1/16, OJ 2018, A70, see "II.E.1.7. Disclaimers" below.
Art. 123(2) EPC applies to all amendments to the patent application or patent. These include corrections of the description, claims or drawings under R. 139, second sentence, EPC (for details, see in this chapter II.E.4. "Correction of errors in the description, claims and drawings").
The Enlarged Board has stressed the importance of applying a uniform concept of disclosure (with reference to Art. 54, 87 and 123 EPC; see G 2/10, OJ 2012, 376, point 4.6 of the Reasons, citing G 1/03, OJ 2012, 436; see also G 1/15, OJ 2017, A82, with reference to G 2/98, OJ 2001, 413). See also e.g. T 330/14.
In the case of divisional applications, the same principles are to be applied for determining whether subject-matter extends beyond the content of the earlier application as filed (G 1/05 date: 2007-06-28, OJ 2008, 271, point 5.1 of the Reasons). The decisions dealing with such cases are therefore also reported in this chapter.
The same principles also apply to the ground for opposition under Art. 100(c) EPC.
The ground for opposition under Art. 100(c) EPC and the corresponding requirement of Art. 123(2) EPC in regard to any amendment carried out on the patent in the course of the opposition and opposition appeal proceedings are of equal fundamental importance compared to other requirements, such as e.g. novelty, inventive step or sufficiency of disclosure, when it comes to deciding whether a patent can be maintained; also, extension of subject-matter in the terms of Art. 123(2) EPC was not a question of "form" of the patent, which might fall under the heading of a "formal requirement", but a substantive one (T 2171/14).