In this case, the original application already indicates that specific subject-matter is not part of the invention.
Negative features help to define the claimed invention in the same way as positive ones, and must be examined on the same basis. In other words, they may confer novelty and, like positive features, are assessed as to their relevance to inventive step. They must also fulfil the requirements of Art. 84 (clarity, conciseness and support), and their inclusion in the claims must not infringe Art. 123(2) (T 170/87, T 365/88).
Negative features, like positive ones, may be structural or functional, and may relate to either a physical entity or an activity.