In particular, provides that a European patent application, or European patent, may not be amended (during prosecution for an application, and after grant for a patent) in such a way that it contains subject-matter which extends beyond the content of the application as filed. The underlying idea of Article 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. This legal provision illustrates the importance accorded by the Convention to the content of a European patent application as filed - i.e. on the filing date - in respect of its legal effects.
An extension of the subject-matter of the European patent beyond the content of the application as filed is a ground of opposition, and revocation.