In element <target>, this attribute must be used if the element is used.

In elements <abbrev>, <abstract>, <ack>, <address>, <aff>, <aff-alternatives>, <alt-text>, <app>, <app-group>, <article-title>, <attrib>, <author-comment>, <award-group>, <bio>, <boxed-text>, <caption>, <chem-struct>, <chem-struct-wrap>, <col>, <colgroup>, <collab>, <compound-kwd>, <contrib>, <contrib-group>, <def>, <def-item>, <def-list>, <disp-formula>, <disp-formula-group>, <disp-quote>, <element-citation>, <ext-link>, <fig>, <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>, <media>, <mixed-citation>, <mml:math>, <named-content>, <nested-kwd>, <nlm-citation>, <p>, <person-group>, <preformat>, <product>, <ref>, <ref-list>, <related-article>, <related-object>, <sec>, <source>, <speech>, <statement>, <std-organization>, <supplementary-material>, <table>, <table-wrap>, <tbody>, <td>, <term>, <tfoot>, <th>, <thead>, <title>, <tr>, <trans-source>, <trans-title>, <verse-group>, and <xref>, this attribute may be used if the element is used.