Nerf is a statistical named entity recognition (NER) tool based on linear-chain conditional random fields (CRFs). It has been adapted to recognize tree-like structures of NEs (i.e., with recursively embedded NEs) by using the joined label tagging method which -- for a particular sentence -- works as follows: CRF model is used to determine the most probable sequence of labels, Extended IOB method is used to decode the sequence into a forerst of NEs. The extended IOB method also provides the inverse encoding function which is needed during the model training.