Defines the type of work being referenced (type of citation), for example, a book is being cited or a journal article is being cited
Some journal DTDs make a distinction between different types of references, for example, using different names and distinct content models for book references, journal references, patent references, etc. This attribute was designed to preserve the information about the type of reference, for those tagged references that explicitly describe their type.
Conversion Note: If the type of reference (<citation> or <nlm-citation>) is not named in the source file, it need not be identified using this attribute.
|book||Book or book series|
|commun||Informal or personal communication, such as a phone call or an email message|
|discussion||Discussion among a group in some forum — public, private, or electronic — which may or may not be moderated, for example, a single discussion thread in a listserv|
|gov||Government publication or government standard|
|list||Listserv or discussion group (as an entity, as opposed to a single discussion thread which uses the value “discussion”)|
|other||None of the listed types.|
|patent||Patent or patent application|
|thesis||Work written as part of the completion of an advanced degree|
|Restriction: This attribute may be specified if the element is used.|