In Europe, a patent claim lacks novelty when its subject matter has been disclosed to the public by publication or otherwise before the filing date of the claim. This is covered in Europe by Article 54(2) of the European Patent Convention (EPC).
Any disclosure relevant to the patentability of a claim under Article 54(2) EPC may be used not only as basis for an allegation that the claim lacks novelty but also as part of an allegation that the claim lacks an inventive step.
This approach is substantially in common with the practice in much of the rest of the world.
By contrast with much of the rest of the world, however, a European patent claim may also lack novelty over a previous European patent application that was filed prior to the filing date of the claim but published after the filing date of the claim. This arises from the provisions of Article 54(3) EPC. Documents that are citable under Article 54(3) EPC are citable for novelty only and not for inventive step.
So, for example, when analysing a European patent claim that was filed on 1 January 2015, any disclosure made in 2014 or earlier will be fully citable against the claim for novelty and inventive step (Article 54(2) EPC).
In addition, a European patent application that was filed on, say, 31 December 2014 (i.e. before the filing date of the claim) but with a publication date of 30 June 2016 (i.e. after the filing date of the claim), would, once published, be citable against the European claim filed on 1 January 2015 for novelty only and not for inventive step (Article 54(3) EPC).
Therefore, in the event of a novelty objection under Article 54(3) EPC, it is possible to overcome that objection by the introduction of a minor feature that would not be sufficient to confer an inventive step over the Article 54(3) citation but which renders the claim just novel.
"the content of European patent applications as filed, the dates of filing of which are prior to the date referred to in paragraph 2 and which were published on or after that date, shall be considered as comprised in the state of the art"
https://www.epo.org/law-practice/legal-texts/html/epc/2016/e/ar54.html