Indicates the unique identifier for an associated element, so that the element’s content may be cross-referenced.
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 Reference for a Private Character element, so that the full glyph data need not be repeated every time the character is used.
The uniqueness of an identifier is not maintained by the XML; thus, a naming convention should be adopted. This identifier will be referenced by other elements; therefore, it is essential that no logical conflicts occur within a single XML file. An identifier string is typically 1-32 characters in length and starts with a letter of the alphabet. (It is an XML rule that identifiers may not start with a digit.)
|An identifier (ID)||A unique identifier for the element. This can be used by an IDREF-style attribute on, for example, a cross-reference <xref> element, to point to the element that has this ID.|
|Restriction: This attribute may be specified if the element is used.|