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.
Keywords 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.
<!ELEMENT kwd (#PCDATA %kwd-elements;)* >
(#PCDATA | email | ext-link | uri | inline-supplementary-material | related-article | related-object | hr | bold | italic | monospace | overline | overline-start | overline-end | roman | sans-serif | sc | strike | underline | underline-start | underline-end | alternatives | inline-graphic | private-char | chem-struct | inline-formula | tex-math | mml:math | abbrev | milestone-end | milestone-start | named-content | styled-content | fn | target | xref | sub | sup | x | break)*
Any combination of:
<article> <front> ... <abstract>... </abstract> <kwd-group kwd-group-type="author"> <kwd>DNA analysis</kwd> <kwd>gene expression</kwd> <kwd>parallel cloning</kwd> <kwd>fluid microarray</kwd> </kwd-group> </article-meta> </front> ...</article>