Metafeatures can be easily implemented, usually in less than 200 lines of code. To add metafeatures, they must implement the interface of the Java class MetafeatureI, which has a total of 8 methods. Most of these are housekeeping functions (e.g. String name() to return a metafeature's name). The most important are setParam(String param, String value) to set the various settings above (e.g. useRelativeTime, etc), and EventVec findEvents(Stream s) that applies the metafeature extraction function to a training stream and returns a vector of events (i.e. instantiated features).