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 the 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.

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 | 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="1.1">
<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">