A keyword is a finding aid used to record one subject term, key phrase, abbreviation, indexing word, taxonomic structure, or other expression that is associated with a whole structure (such as an article). Keywords can be used for identification, searching, and indexing purposes. A keyword element (<kwd>) may contain a repetition of words found in the structure, or it may contain broader terms, narrower terms, related terms, or taxonomic identifiers used to find the structure in a search or provide semantic classification of the text by mapping a specific structure to a taxonomy.


Key words are contained in <kwd-group>s. There may be several <kwd-group>s, each of which can be identified separately by language, vocabulary, or taxonomy source. None of the individual keyword elements (<kwd>, <compound-kwd>, <nested-kwd>) take the @xml:lang attribute; that is reserved for the <kwd-group>. This means that keywords must be sorted by language and entered in language groups.
Related Essay: For a discussion on the use of <kwd>, see Keywords.
Best Practice: In this Tag Set, nested keywords (<nested-kwd>) should be reserved for hierarchical material such as taxonomies. There are a few journal/book tag sets in which keyword nesting is used to simulate a two-part list. Such a keyword list should be tagged as a <def-list> instead.
Attribute Best Practice: If the content of the <kwd> element is a term from a controlled vocabulary (ontology, taxonomy, term-list, vocabulary, industry glossary, or other known source), the vocabulary attributes should be used to identify that source. The source named can be a formal ontology or an informal field of study.
Term Identification Attributes: Two attributes are used in this Tag Set to identify an individual term from a vocabulary (controlled or an uncontrolled):
The content of the element is the display version of the vocabulary or taxonomic term. The @vocab-term attribute holds the canonical version of the same term, as it appears in the vocabulary. For example, if the attribute value is “digitized-vor”, the element might contain the display text “Digitized Version of Record”.
Unique identifier of the term within a specific vocabulary, such as (but not limited to) an item number, a URI, DOI, etc.
Vocabulary Identification Attributes: Two attributes are used in this Tag Set to identify a vocabulary. If these attributes have already been used on <kwd-group>, they need not be repeated on each <kwd>.
Name of the controlled or uncontrolled vocabulary, taxonomy, ontology, index, database, or similar that is the source of the term. For example, for a subject term, a value might be the IPC Codes (“ipc”) or MESH headings (“mesh”). For an uncontrolled term, the value might be an area of study such as “medical-devices” or merely the word “uncontrolled”.
Unique identifier of the vocabulary, such as (but not limited to) a URI or DOI. For example, for Dublin Core (DCC), the identifier may be “http://dublincore.org/documents/2012/06/14/dces/”.

Related Elements

This Tag Set contains several differently-structured types of keywords:
  • The element <kwd> is used with simple keywords: words or phrases.
  • The element <compound-kwd> is used with multi-part keywords, such as a keyword that is a code-and-term pair.
  • The element <nested-kwd> is used with hierarchical keywords structures, such as taxonomies, to record a portion of a taxonomic hierarchy. Both simple and compound keywords can be nested hierarchically.


Content Model

<!ELEMENT  kwd          (#PCDATA %kwd-elements;)*                    >

Expanded Content Model

(#PCDATA | bold | fixed-case | italic | monospace | overline | roman | sans-serif | sc | strike | underline | ruby | abbrev | index-term | index-term-range-end | named-content | styled-content | sub | sup)*


This element may be contained in:

Example 1

An author’s list of keywords for a document:
<article dtd-version="1.2">
<kwd-group kwd-group-type="author">
<kwd>DNA analysis</kwd>
<kwd>gene expression</kwd>
<kwd>parallel cloning</kwd>
<kwd>fluid microarray</kwd>

Example 2

Multiple keyword groups for a document (including Japanese):
<kwd-group xml:lang="en">
<kwd>heated air</kwd>

<kwd-group xml:lang="ja">