This code system http://terminology.hl7.org/CodeSystem/citation-variant-type defines the following codes:

Code Display Definition
version version Denotes a specific version of an article or artifact.
subpart subpart Denotes a specific portion of an article, such as page, section, paragraph, line, table or figure.
supplement Supplement or Appendix Used to denote a supplementary file, appendix, or additional part that is not a subpart of the primary article.
supplement-subpart Supplement or Appendix Subpart Used to denote a subpart within a supplementary file or appendix.
base-for-article-set Base citation for an article set Used to define the base citation or an article set with individual articles as variant citations.
article-set Part of an article set Used to distinguish an individual article within an article set where the article set is a base citation.
<status value="draft"/> <experimental value="false"/> <date value="2020-08-20T17:41:31+10:00"/> <publisher value="HL7 (FHIR Project)"/> <contact> <telecom> <system value="url"/> <value value="http://hl7.org/fhir"/> </telecom> <telecom> <system value="email"/> <value value="fhir@lists.hl7.org"/> </telecom> </contact> <description value="To describe the reason for the variant citation, such as version number or subpart specification."/> <caseSensitive value="true"/> <valueSet value="http://hl7.org/fhir/ValueSet/citation-variant-type"/> <content value="complete"/> <concept> <code value="version"/> <display value="version"/> <definition value="Denotes a specific version of an article or artifact."/> </concept> <concept> <code value="subpart"/> <display value="subpart"/> <definition value="Denotes a specific portion of an article, such as page, section, paragraph, line, table or figure."/> </concept> <concept> <code value="supplement"/> <display value="Supplement or Appendix"/> <definition value="Used to denote a supplementary file, appendix, or additional part that is not a subpart of the primary article."/> </concept> <concept> <code value="supplement-subpart"/> <display value="Supplement or Appendix Subpart"/> <definition value="Used to denote a subpart within a supplementary file or appendix."/> </concept> <concept> <code value="base-for-article-set"/> <display value="Base citation for an article set"/> <definition value="Used to define the base citation or an article set with individual articles as variant citations."/> </concept> <concept> <code value="article-set"/> <display value="Part of an article set"/> <definition value="Used to distinguish an individual article within an article set where the article set is a base citation."/> </concept> </CodeSystem>