Optional features, i.e. features preceded by expressions such as "preferably", "for example", "such as" or "more particularly" are allowed if they do not introduce ambiguity. In such a case, they are to be regarded as entirely optional.
These expressions introduce ambiguity and render the scope of the claim unclear if they do not lead to a restriction of the subject-matter of the claim.
For example, the wording "a method to manufacture an artificial stone, such as a clay brick" does not fulfil the requirements of Art. 84, because a clay brick will never be an artificial stone. Hence it is unclear if either an artificial stone or a clay brick is manufactured by the method of the claim.
Analogously, the wording "the solution is heated up to between 65 and 85°C, particularly to 90°C" does not fulfil the requirements of Art. 84 because the temperature after the term "particularly" contradicts the range before it.