In elements <abbrev>, <app>, <award-id>, <bio>, <chem-struct>, <collab>, <contrib>, <custom-meta>, <element-citation>, <email>, <ext-link>, <extended-by>, <funding-source>, <graphic>, <inline-graphic>, <inline-media>, <inline-supplementary-material>, <institution>, <issue-id>, <license>, <long-desc>, <media>, <mixed-citation>, <named-content>, <nlm-citation>, <pronunciation>, <pub-id>, <related-article>, <related-object>, <restricted-by>, <self-uri>, <std>, <supplementary-material>, <uri>, and <volume-id>, this attribute may be used if the element is used.
| Value |
Meaning |
| An alphanumeric string, which may include hyphens |
An abbreviation for a natural language (such as en for English or de for German) or for a language and a script (ja-Kana ). |