This code system http://hl7.org/fhir/artifact-url-classifier defines the following codes:

CodeDisplayDefinition
abstract AbstractThe URL will reach a brief summary for the article.
full-text Full-TextThe URL will reach the full-text of the article.
supplement SupplementThe URL will reach a supplement, appendix, or additional supporting information for the article.
webpage WebpageThe URL will reach a webpage related to the article, where the content is not easily classified as abstract, full-text or supplement.
file-directory File directoryThe URL will reach a file directory.
code-repository Code repositoryFile archive and web hosting facility for source code of software, documentation, web pages, and other works.
restricted RestrictedThe URL content has restricted access (e.g. subcription required).
compressed-file Compressed fileCompressed archive file (e.g. a zip file) that contains multiple files
doi-based DOI BasedThe URL is derived from the Digital Object Identifier (DOI).
pdf PDFThe URL will reach content in PDF form.
json JSONThe URL will reach content in JSON format.
xml XMLThe URL will reach content in XML format.
version-specific Version SpecificThe URL will reach content that is a specific version of the article.
computable-resource Computable resourceThe URL will reach content that is machine-interpretable.
not-specified Not SpecifiedUsed when URL classifier is not specified but expected in a system.
<status value="active"/><experimental value="false"/><date value="2020-12-28T16:55:11+11:00"/><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="Code the reason for different URLs, eg abstract and full-text."/><jurisdiction><coding><system value="http://unstats.un.org/unsd/methods/m49/m49.htm"/><code value="001"/><display value="World"/></coding></jurisdiction><caseSensitive value="true"/><valueSet value="http://hl7.org/fhir/ValueSet/artifact-url-classifier"/><content value="complete"/><concept><code value="abstract"/><display value="Abstract"/><definition value="The URL will reach a brief summary for the article."/></concept><concept><code value="full-text"/><display value="Full-Text"/><definition value="The URL will reach the full-text of the article."/></concept><concept><code value="supplement"/><display value="Supplement"/><definition value="The URL will reach a supplement, appendix, or additional supporting information for the article."/></concept><concept><code value="webpage"/><display value="Webpage"/><definition value="The URL will reach a webpage related to the article, where the content is not easily classified as abstract, full-text or supplement."/></concept><concept><code value="file-directory"/><display value="File directory"/><definition value="The URL will reach a file directory."/></concept><concept><code value="code-repository"/><display value="Code repository"/><definition value="File archive and web hosting facility for source code of software, documentation, web pages, and other works."/></concept><concept><code value="restricted"/><display value="Restricted"/><definition value="The URL content has restricted access (e.g. subcription required)."/></concept><concept><code value="compressed-file"/><display value="Compressed file"/><definition value="Compressed archive file (e.g. a zip file) that contains multiple files"/></concept><concept><code value="doi-based"/><display value="DOI Based"/><definition value="The URL is derived from the Digital Object Identifier (DOI)."/></concept><concept><code value="pdf"/><display value="PDF"/><definition value="The URL will reach content in PDF form."/></concept><concept><code value="json"/><display value="JSON"/><definition value="The URL will reach content in JSON format."/></concept><concept><code value="xml"/><display value="XML"/><definition value="The URL will reach content in XML format."/></concept><concept><code value="version-specific"/><display value="Version Specific"/><definition value="The URL will reach content that is a specific version of the article."/></concept><concept><code value="computable-resource"/><display value="Computable resource"/><definition value="The URL will reach content that is machine-interpretable."/></concept><concept><code value="not-specified"/><display value="Not Specified"/><definition value="Used when URL classifier is not specified but expected in a system."/></concept></CodeSystem>