Methods. The Methods section appears in most online original research articles and should contain all elements necessary for interpretation and replication of the results. Methods should be written as concisely as possible and typically do not exceed 3,000 words but may be longer if necessary. Methods-only references do not count against your reference limit. We encourage you to deposit any step-by-step protocols used in your study in Protocol Exchange, an open resource maintained by Nature Research. These protocols are linked to the Methods section upon publication.