TEI (Text Encoding
Initiative) is a large, elaborate DTD used primarily in academia for
computer transcription of literary texts. TEI's Unix-based toolchains
use many of the same tools that are involved with DocBook, but with
different stylesheets and (of course) a different DTD.
XHTML, the latest version of HTML, is also an XML application
described by a DTD, which explains the family resemblance between
XHTML and DocBook tags. The XHTML toolchain consists of Web browsers
that can format HTML as flat ASCII, together with any of a number of
ad-hoc HTML-to-print utilities.
Many other XML DTDs are maintained to help people exchange
structured information in fields as diverse as bioinformatics and
banking. You can look at a list of
repositories to get some idea of the variety available.
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