id

Document Internal Identifier

Unique internal identifier of an element; allows element to be cross-referenced (made into a link). Value must be unique across a document, not just for an element type.

Remarks

The ID and IDREF attribute values form a primitive reference mechanism for XML that allow internal linking, for example, from a reference in the text to a figure or a table. As another 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.)

External Identifiers: This attribute holds an internal document identifier that can be used by software to perform a simple link. It should not be confused with elements such as <book-id>, <contrib-id>, and <institution-id> that are used to hold externally defined identifiers such as a DOI (for the book id), an ORCID personal identifier (for the contributor id), or a Ringgold identifier (for an institution id).

Attribute Values

In Elements

<overline-start>
<target>
<underline-start>
ValueMeaning
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 is required; it must be used in the document.

In Elements

<abbrev>, <abstract>, <ack>, <addr-line>, <address>, <aff>, <aff-alternatives>, <alt-text>, <alt-title>, <alternatives>, <annotation>, <anonymous>, <answer>, <answer-set>, <app>, <app-group>, <array>, <article-title>, <attrib>, <author-comment>, <author-notes>, <award-group>, <award-id>, <back>, <bio>, <body>, <bold>, <book>, <book-back>, <book-body>, <book-id>, <book-meta>, <book-part>, <book-part-id>, <book-part-meta>, <book-part-wrapper>, <book-title>, <book-title-group>, <book-volume-id>, <book-volume-number>, <boxed-text>, <break>, <caption>, <chapter-title>, <chem-struct>, <chem-struct-wrap>, <citation-alternatives>, <code>, <col>, <colgroup>, <collab>, <collab-alternatives>, <collection-id>, <collection-meta>, <comment>, <compound-kwd>, <compound-kwd-part>, <compound-subject>, <compound-subject-part>, <conf-acronym>, <conf-date>, <conf-loc>, <conf-name>, <conf-num>, <conf-sponsor>, <conf-theme>, <conference>, <contrib>, <contrib-group>, <contrib-id>, <copyright-holder>, <copyright-statement>, <copyright-year>, <corresp>, <count>, <country>, <counts>, <custom-meta>, <custom-meta-group>, <date>, <date-in-citation>, <day>, <dedication>, <def>, <def-head>, <def-item>, <def-list>, <degrees>, <disp-formula>, <disp-formula-group>, <disp-quote>, <edition>, <element-citation>, <elocation-id>, <email>, <equation-count>, <era>, <etal>, <event>, <event-desc>, <explanation>, <ext-link>, <fax>, <fig>, <fig-count>, <fig-group>, <fixed-case>, <floats-group>, <fn>, <fn-group>, <foreword>, <fpage>, <front-matter>, <front-matter-part>, <funding-group>, <funding-source>, <funding-statement>, <given-names>, <glossary>, <glyph-data>, <glyph-ref>, <gov>, <graphic>, <hr>, <index>, <index-div>, <index-entry>, <index-group>, <index-term>, <index-term-range-end>, <inline-formula>, <inline-graphic>, <inline-supplementary-material>, <institution>, <institution-id>, <institution-wrap>, <isbn>, <issn>, <issn-l>, <issue>, <issue-id>, <issue-part>, <issue-title>, <italic>, <journal-id>, <kwd>, <kwd-group>, <label>, <license>, <license-p>, <list>, <list-item>, <long-desc>, <lpage>, <media>, <meta-name>, <meta-value>, <milestone-end>, <milestone-start>, <mixed-citation>, <mml:math>, <monospace>, <month>, <name>, <name-alternatives>, <named-book-part-body>, <named-content>, <nav-pointer>, <nav-pointer-group>, <nested-kwd>, <note>, <notes>, <object-id>, <on-behalf-of>, <open-access>, <overline>, <overline-end>, <p>, <page-count>, <page-range>, <part-title>, <patent>, <permissions>, <person-group>, <phone>, <preface>, <prefix>, <preformat>, <price>, <principal-award-recipient>, <principal-investigator>, <private-char>, <product>, <pub-date>, <pub-history>, <pub-id>, <publisher>, <publisher-loc>, <publisher-name>, <question>, <question-wrap>, <rb>, <ref>, <ref-count>, <ref-list>, <related-article>, <related-object>, <role>, <roman>, <rp>, <rt>, <ruby>, <sans-serif>, <sc>, <season>, <sec>, <sec-meta>, <see>, <see-also>, <see-also-entry>, <see-entry>, <self-uri>, <series>, <sig>, <sig-block>, <size>, <source>, <speaker>, <speech>, <statement>, <std>, <std-organization>, <strike>, <string-conf>, <string-date>, <string-name>, <styled-content>, <sub>, <subj-group>, <subject>, <subtitle>, <suffix>, <sup>, <supplement>, <supplementary-material>, <surname>, <table>, <table-count>, <table-wrap>, <table-wrap-foot>, <table-wrap-group>, <tbody>, <td>, <term>, <term-head>, <tex-math>, <textual-form>, <tfoot>, <th>, <thead>, <title>, <title-group>, <toc>, <toc-div>, <toc-entry>, <toc-group>, <tr>, <trans-abstract>, <trans-source>, <trans-subtitle>, <trans-title>, <trans-title-group>, <underline>, <underline-end>, <unstructured-kwd-group>, <uri>, <verse-group>, <verse-line>, <volume>, <volume-id>, <volume-in-collection>, <volume-number>, <volume-series>, <volume-title>, <word-count>, <x>, <xref>, <year>
ValueMeaning
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 is an optional attribute; there is no default.