Indicates the unique identifier for an associated element, so that the element’s content may be cross-referenced. IDs must be unique inside their document (not just within their element type), and the XML parser enforces this.
The ID and IDREF attribute values constitute a primitive reference mechanism for XML. For example, when an @id attribute has been used on a <glyph-data> element, that identifier can be referenced by an IDREF-style attribute on a <glyph-ref> element, so that the full glyph data can be pointed to and need not be repeated every time the character is used.
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.)
This attribute (@id) has been significantly remodeled in version 3.0 of the Tag Set. For a few elements, the values and/or usage in version 3.0 are not backward-compatible with that in previous versions of the Tag Set. 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. An XML parser can verify that an IDREF-style attribute 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. An XML parser can verify that an IDREF-style attribute pointing to one of these is pointing to a valid ID. |
Restriction: This attribute may be specified if the element is used. |