Attribute: NlmCategory
Specifies the NLM Category assigned by NLM to the subsections of a structured abstract. "Unassigned" is used for structured abstract headings that do not map to one of NLM's specific categories. This attribute is not applied to an structured abstract headings for <BookDocument> citations.
In <AbstractText>
NlmCategory (BACKGROUND|OBJECTIVE|METHODS|RESULTS|CONCLUSIONS|UNASSIGNED) #IMPLIED