A system including a server, a search engine, and one or more user devices is used to analyse data files. The user devices may be used to effect a search, such as a search for documents, websites or other material. A search request is effected on the user device and forwarded to the server. A subject data file is obtained which represents a document. The subject data file is searched for instances of data representing user selected target features. The detected instances which include one or more of features indicative of a list and features indicative of content relating to a casual convention, are changed to be perceptibly different from features which are not target features when the modified data files is provided to the user.