id

Identifier

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.

Usage

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.

Remarks

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.

Attribute Values

In Elements

<overline-start>
<target>
<underline-start>
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.

In Elements

<abbrev>, <abstract>, <ack>, <address>, <aff>, <alt-text>, <app>, <app-group>, <array>, <article-title>, <attrib>, <author-comment>, <author-notes>, <award-group>, <bio>, <book-part>, <book-title>, <boxed-text>, <caption>, <chem-struct>, <chem-struct-wrap>, <col>, <colgroup>, <collab>, <collection>, <collection-member>, <compound-kwd>, <contrib>, <contrib-group>, <corresp>, <custom-meta>, <def>, <def-item>, <def-list>, <disp-formula>, <disp-formula-group>, <disp-quote>, <element-citation>, <ext-link>, <fig>, <fig-group>, <fn>, <fn-group>, <funding-source>, <glossary>, <glyph-data>, <graphic>, <inline-formula>, <inline-graphic>, <inline-supplementary-material>, <institution>, <kwd>, <kwd-group>, <list>, <list-item>, <long-desc>, <map-group>, <media>, <milestone-end>, <milestone-start>, <mixed-citation>, <mml:math>, <named-content>, <nlm-citation>, <note>, <notes>, <p>, <person-group>, <preformat>, <product>, <ref>, <ref-list>, <related-article>, <related-object>, <sec>, <sig>, <sig-block>, <source>, <speech>, <statement>, <supplementary-material>, <table>, <table-wrap>, <table-wrap-group>, <tbody>, <td>, <term>, <tex-math>, <tfoot>, <th>, <thead>, <title>, <tr>, <trans-abstract>, <trans-source>, <trans-title>, <trans-title-group>, <verse-group>, <xref>
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.