If a supplemental structure can be tagged as an XML element, it should be tagged as one, with the attribute @supplemental set to "yes". For example, if the supplemental object is a figure, it should be tagged as a JATS <fig> element and flagged as supplementary (<fig supplemental="yes" ...>). Other than the @supplemental attribute, there is no distinction between the content of a supplementary object and an integral object. The @supplemental attribute is allowed on the following content elements, so any of these elements can be an integral part of the article or a supplementary object.

Examples of content that might be supplementary include resources such as the following:

• The last several figures of the article that could not be included as part of the base article for stylistic considerations, editorial policy, or space limitations;
• Special sections that are not part of the flow of the narrative, but discuss important supplemental matters such as measurements or methods;
• “Extra” tables that do not display with the work, but that record the measurements on which the article is based (for example, tables that need to be available so the peer reviewers can check the article content);
• Material added to the work for enhancement purposes, such as a quiz or a form that can be filled out or copied.

If a link in the text of an article points to an external supplementary object, such as a video or a .jpeg image, the link should be tagged using one of the JATS external object linking elements, with the attribute @supplemental set to "yes". For example, if the supplemental object is a still image, it should be tagged as a JATS <graphic> element and flagged as supplementary (<graphic supplemental="yes" .../>).

The @supplemental attribute is allowed on the following linked elements:

Each supplementary linked element points to its object using @xlink:href and may describe the object using other attributes such as @mimetype.

Examples of linked objects that might be supplementary include resources such as the following:

• Material added to the work for enhancement purposes such as pronunciation files, a 3-minute video version of the chemical reaction that was described in the article with narrative, still images in many sizes and formats, and similar material (This material tends to be in graphics formats such as MP4 or .png files.)
• Voluminous material (such as a genomic database or the multiple data sets behind a work that abstracts the highlights of those datasets) that supports the conclusions of the narrative but can never accompany an article based on sheer mass
• Code sets and applications

Note: An object that cannot be fully represented in print or static HTML page (such as a movie, sound file, or animation) should not automatically be considered supplemental. If the object is necessary for understanding the article (in other words, the object is “integral” as defined by NISO RP-15-2013, discussed below), it should be tagged at the appropriate location in the text using one of the <graphic>, <media>, or <ext-link> elements, without a @supplemental attribute.

NISO RP-15-2013 Recommended Practices for Online Supplemental Journal Article Materials (https://www.niso.org/apps/group_public/download.php/10055/RP-15-2013_Supplemental_Materials.pdf) and NISO JATS have identical concepts for “additional” and “integral” material that comprises an article.

Both NISO JATS and NISO RP-15-2013 define:

• integral content as “material that is essential for the full understanding of the article by the general scientist or reader in the journal’s discipline”, and
• additional content as “supplemental material that provides additional, relevant, and useful expansion of the article in the form of text, tables, figures, multimedia, or data, and that may aid any reader to achieve deeper understanding of the current work through added detail and context. [Such] additional content … is not essential to the understanding of the article.”

In prior versions of JATS, the Supplementary Material Metadata (now deprecated <supplementary-material>) element had two uses: inside text to describe a supplementary object at a particular place in the narrative and inside metadata (<article-meta>) to name a supplemental object associated with the article and provide a link to it. For example, a metadata <supplementary-material> element might have contained a description of an animation, including the title of the animation, a description of the rationale for the animation, and the first frame of the animation (tagged as a <graphic> element). Both textual and metadata uses are now deprecated.

• Supplementary Material Content — For textual objects (such as tables, figures, and sections), the JATS element containing the material should be placed directly into the article, and the element identified as “@supplemental="yes"”. How this material is presented or counted is not defined by JATS, and will need to be decided by the application.
• Linking to a Supplementary Object — In prior versions of JATS, <supplementary-material> was used as an alert to the existence of supplementary material, so that such material could be accessed from the article. Modern best practice is to tag such a link directly as a <graphic> or <media> object or to create an external link using <ext-link>.