Indicates the type of element to which a cross reference is pointing (e.g., to a figure, an author note, a bibliographic reference citation, etc.). These values may be used for type-specific processing or validation.
The <xref> element may be used to reference anything that has an Identifier id attribute. This single element takes the place of the many named types of references (such as figure references, table references, and footnote references) that are common in many journal DTDs. This attribute preserves the information from such DTDs concerning the type of element to which the cross-reference is pointing.
|bibr||Bibliographic reference (to a <citation>, <nlm-citation>, or <ref> element).|
|boxed-text||Textbox or sidebar.|
|chem||Chemical structure wrapper or chemical structure.|
|fig||Figure or figure group.|
|table-fn||A Footnote (<fn>) element that is found within a <table-wrap> element. Such footnotes should be displayed with the table rather than, for example, at the bottom of the page or screen.|
|other||Something other than the named reference types.|
|Restriction: This attribute may be specified if the element is used.|