Type of Cross Reference

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 tag sets. This attribute preserves the information from such tag sets concerning the type of element to which the cross-reference is pointing.

Attribute Values

In Element

Value Meaning
aff Affiliation
app Appendix
bibr Bibliographic reference (typically to a <ref> element, but it may point to a <element-citation> or <mixed-citation> if there are multiple citations inside the <ref> element).
boxed-text Textbox or sidebar
chem Chemical structure (to a <chem-struct> or <chem-struct-wrap> element)
contrib Contributor
corresp Corresponding author
disp-formula Display formula
fig Figure (to a <fig> element)
fn Footnote
kwd Keyword
list List or list item (to a <list> or <list-item> element; also, possibly to a <def-list> or <def-item> element)
other None of the items listed
plate Plate
scheme Scheme
sec Section
statement Statement
supplementary-material Supplementary information
table Table (to a <table-wrap> element)
table-fn Table footnote
Restriction: This attribute may be specified if the element is used.