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 <oasis:table> element, that identifier can be referenced by an IDREF-style attribute on a <xref> element, so that the full table 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.)
|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.|