additional-docidentifier: metanorma/metanorma-iso#1104

author/ref/document-attributes.adoc

@@ -149,6 +149,13 @@ identifier [added in https://github.com/metanorma/metanorma-standoc/releases/tag
 This value is used for document identifiers that do not follow normal SDO conventions,
 including for documents that are adoptions from other SDOs. 
 
+`:additional-docidentifier:`::
+This attribute provides additional primary identifiers for the document, to be used alongside
+the native identifier generated from `docnumber` or `docidentifier` [added in https://github.com/metanorma/metanorma-standoc/releases/tag/v2.8.2].
+It is intended for copublished standards with multiple primary identifiers.
+The list of identifiers is comma-delimited, and is specified as TYPE:VALUE; e.g.
+`:additional-docidentifier: IDF:IDF 21, RFC:RFC 97`
+
 `:edition:`::
 The document edition.