The examining division has raised an objection under Article 84 that the claims are missing an essential feature (see F‑IV, 4.5).
Unless the applicant is able to demonstrate to the satisfaction of the examining division that the indicated feature is not essential for carrying out the invention, the examining division will normally not admit under Rule 137(3) any further set of claims not containing the feature in question.
Source: http://www.epo.org/law-practice/legal-texts/html/guidelines/e/h_ii_2_3_1_3.htm
Date retrieved: 17 May 2021