Any patent document bearing a filing or priority date earlier than the filing date of the application searched (not the priority date – see B‑VI, 3, and B‑XI, 4) but published on or after that date and the content of which would constitute prior art relevant to novelty (Art. 54(1)) is indicated by the letter "E". Where the patent document and the application searched have the same date (see G‑IV, 5.4), the patent document is also identified by the letter "E". An exception is made for patent documents based on the claimed priority under consideration; these documents are not cited.[Art. 54(3); Art. 139(2); ]
Source: http://www.epo.org/law-practice/legal-texts/html/guidelines/e/b_x_9_2_6.htm
Date retrieved: 17 May 2021