Unique internal identifier of an element; allows element to be cross-referenced (made into a link). Value must be unique across a document, not just for an element type.
The ID and IDREF attribute values constitute a primitive reference mechanism for XML. For example, when an @id attribute has been used on a <fig> element, that identifier can be referenced by an IDREF-style attribute on a <xref> element, so that the figure can be pointed to and need not be repeated every time the figure is mentioned.
An identifier string is typically 1-32 characters in length and must start with a letter of the alphabet. (It is an XML rule that identifiers may not start with a digit.)
Historical Note: This attribute (@id) was significantly remodeled from previous versions of this Tag Set. The current NISO JATS values are backwards compatible with the last NLM version, but not with earlier versions. Specifically, in prior versions the <def-list>, <list>, <list-item>, and tex-math elements permitted this attribute to have any value (CDATA), not only valid XML ID values.
| Value | Meaning |
|---|---|
| An XML identifier (ID) | A unique identifier for the element. XML parsers can verify that an element pointing to one of these is pointing to a valid ID. |
| Restriction: | |
| Value | Meaning |
|---|---|
| An XML identifier (ID) | A unique identifier for the element. XML parsers can verify that an element pointing to one of these is pointing to a valid ID. |
| Restriction: | |