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.

Usage/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.)
ID/IDREF
The ID and IDREF attribute values constitute a primitive reference mechanism for XML that allows internal linking. 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.
External Identifiers
This attribute holds an internal document identifier that can be used by software to perform a simple link. An @id should not be confused with elements such as <article-id>, <contrib-id>, and <institution-id> that are used to hold externally defined identifiers such as a DOI (for the article id), an ORCID personal identifier (for the contributor id), or a Ringgold identifier (for an institution id).
NLM DTD Historical Note
This attribute (@id) was significantly remodeled from previous versions of this Tag Set. The current NISO JATS values are backward compatible with all JATS versions and with the last NLM version (NLM 3.0), but not with earlier NLM DTD versions. Specifically, in prior versions the <def-list>, <list>, <list-item>, and <tex-math> elements permitted this attribute to have any value (CDATA), rather than only valid XML ID values.
REQUIRED on element: <target>
Value Meaning
An XML identifier (ID) A unique identifier for the element. XML parsers can verify that an element pointing to one of these is pointing to a valid ID.
Restriction @id is required; it must be provided if the element is used.
OPTIONAL on many elements; click for list and usage

<abbrev>, <abbrev-journal-title>, <abstract>, <access-date>, <ack>, <addr-line>, <address>, <aff>, <aff-alternatives>, <ali:free_to_read>, <ali:license_ref>, <alt-text>, <alt-title>, <alternatives>, <annotation>, <anonymous>, <answer>, <answer-set>, <app>, <app-group>, <array>, <article>, <article-categories>, <article-id>, <article-meta>, <article-title>, <article-version>, <article-version-alternatives>, <attrib>, <author-comment>, <author-notes>, <award-desc>, <award-group>, <award-id>, <award-name>, <back>, <bio>, <block-alternatives>, <body>, <bold>, <boxed-text>, <break>, <caption>, <chapter-title>, <chem-struct>, <chem-struct-wrap>, <citation-alternatives>, <city>, <code>, <col>, <colgroup>, <collab>, <collab-alternatives>, <collab-name>, <collab-name-alternatives>, <collab-wrap>, <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>, <content-language>, <contrib>, <contrib-group>, <contrib-id>, <contributed-resource-group>, <copyright-holder>, <copyright-statement>, <copyright-year>, <corresp>, <count>, <country>, <counts>, <custom-meta>, <custom-meta-group>, <data-title>, <date>, <date-in-citation>, <day>, <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>, <extended-by>, <fax>, <fig>, <fig-count>, <fig-group>, <fixed-case>, <floats-group>, <fn>, <fn-group>, <fpage>, <front>, <front-stub>, <funding-group>, <funding-source>, <funding-statement>, <given-names>, <glossary>, <glyph-data>, <glyph-ref>, <gov>, <graphic>, <history>, <hr>, <index-term>, <index-term-range-end>, <inline-formula>, <inline-graphic>, <inline-media>, <inline-supplementary-material>, <institution>, <institution-id>, <institution-wrap>, <isbn>, <issn>, <issn-l>, <issue>, <issue-id>, <issue-part>, <issue-sponsor>, <issue-subtitle>, <issue-title>, <issue-title-group>, <italic>, <journal-id>, <journal-meta>, <journal-subtitle>, <journal-title>, <journal-title-group>, <kwd>, <kwd-group>, <label>, <legend>, <license>, <license-p>, <list>, <list-item>, <long-desc>, <lpage>, <media>, <meta-name>, <meta-value>, <milestone-end>, <milestone-start>, <mixed-citation>, <monospace>, <month>, <name>, <name-alternatives>, <named-content>, <nested-kwd>, <nlm-citation>, <note>, <notes>, <object-id>, <on-behalf-of>, <open-access>, <option>, <overline>, <p>, <page-count>, <page-range>, <part-title>, <patent>, <permissions>, <person-group>, <phone>, <postal-code>, <prefix>, <preformat>, <price>, <principal-award-recipient>, <principal-investigator>, <private-char>, <processing-meta>, <product>, <pub-date>, <pub-date-not-available>, <pub-history>, <pub-id>, <publisher>, <publisher-loc>, <publisher-name>, <question>, <question-preamble>, <question-wrap>, <question-wrap-group>, <rb>, <ref>, <ref-count>, <ref-list>, <related-article>, <related-object>, <resource-group>, <resource-id>, <resource-name>, <resource-wrap>, <response>, <restricted-by>, <role>, <roman>, <rt>, <ruby>, <sans-serif>, <sc>, <season>, <sec>, <sec-meta>, <see>, <see-also>, <self-uri>, <series>, <series-text>, <series-title>, <sig>, <sig-block>, <size>, <source>, <speaker>, <speech>, <state>, <statement>, <std>, <std-organization>, <strike>, <string-date>, <string-name>, <styled-content>, <sub>, <sub-article>, <subj-group>, <subject>, <subtitle>, <suffix>, <sup>, <supplement>, <supplementary-material>, <support-description>, <support-group>, <support-source>, <surname>, <table>, <table-count>, <table-wrap>, <table-wrap-foot>, <table-wrap-group>, <tbody>, <td>, <term>, <term-head>, <tex-math>, <textual-form>, <tfoot>, <th>, <thead>, <time-stamp>, <title>, <title-group>, <tr>, <trans-abstract>, <trans-source>, <trans-subtitle>, <trans-title>, <trans-title-group>, <underline>, <uri>, <verse-group>, <verse-line>, <version>, <volume>, <volume-id>, <volume-issue-group>, <volume-series>, <word-count>, <xref>, <year>

Value Meaning
An XML identifier (ID) A unique identifier for the element. XML parsers can verify that an element pointing to one of these is pointing to a valid ID.
Restriction @id is an optional attribute; there is no default.
Tagged Samples
Footnote identifiers
...
<fn-group>
 <fn id="TF1150"><p>Data not available for 1 trial.</p></fn>
 <fn id="TF1-151"><p>P %lt; 0.05 (random effects model).</p></fn>
</fn-group>
...
Identifier for a figure, showing a reference to the figure (from an <xref> element)
...  
<p>Allocation of tags to individual molecules is outlined in
 <xref ref-type="fig" rid="F2" alt="figure two">Fig.&#x00A0;2</xref>.
 First, the complete repertoire of tags ...</p> 
<fig id="F2">...</fig>
...