Unique identifier of an element; allows element to be cross-referenced. 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 for NLM 3.0. The current JATS values are backwards compatible with NLM 3.0 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: This attribute must be specified if the element is used. | |
| 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: This attribute may be specified if the element is used. | |