The only new element created for the Publishing DTD, the highly structured NLM citation, used to enforce a slightly loose version of an NLM-structured bibliographic reference. Sequence is enforced and interior punctuation is expected to be generated. With Version 2.3, this element was added to the Book, Book Collection, and Historical Tag Sets.
<!ENTITY % nlmcitation.ent PUBLIC "-//NLM//DTD NLM Citation v2.3 20070202//EN" "nlmcitation.ent" >
bookcustom-modules.ent