In Metadata: In the article metadata, the article subtitle and title are identified separately and tagged with two different elements, the <article-title> and <subtitle> elements.

In Citations: Within a bibliographic reference citation, the subtitle of a document cannot be preserved separately as this Tag Set identifies no cited-subtitle elements. How the subtitle should be tagged depends on how the citation is tagged.

For references tagged with either the <element-citation> or the <nlm-citation> elements, since these two models do not permit untagged text there are two choices:

• The subtitle may be included with the title inside the <article-title> element for journal articles or inside the <source> element for book titles, proceedings titles, and other titles, or
• The subtitle may be tagged as <named-content> with a @content-type of “subtitle”.

For references tagged with the <mixed-citation> element, there are three choices:

• The subtitle may be included with the title inside the <article-title> element for journal articles or inside the <source> element for book titles, proceedings titles, and other titles,
• The subtitle may be left as untagged data characters within the text of the reference, or
• The subtitle may be tagged as <named-content> with a @content-type of “subtitle”.

Best Practice In Citations: Although this Tag Set cannot enforce either practice, retrieval performance will be enhanced if the subtitle for all cited material is consistently placed within the <article-title> element for journal articles and within the <source> element for book titles, proceedings titles, and other documents. When marked as either a <named-content> or left as untagged text, the subtitle is easy to lose to searching. It is also not always easy to identify, particularly with historical or foreign material, which part of a multipart title is the main title and which the subtitle.