3.8 Search on dependent claims 

However, where there is doubt about whether the independent claim's subject-matter is patentable, the search may have to be continued in other parts of the documentation, e.g. in one or more additional classification units, in order to assess whether the subject-matter of the dependent claim as such is novel and involves an inventive step. No special search is carried out for features that seem prima facie trivial or are generally known in the art. However, a handbook or other document showing that a feature is generally known can be cited if it can be found quickly (see G‑VII, 6(iii)). A dependent claim that adds another feature (instead of providing more detail on something already in the independent claim) has to be considered in combination with the features in the independent claim and is dealt with accordingly (see F‑IV, 3.4).