 | Level: Intermediate Contributors: W3C 06 Feb 2007
Updated 25 Apr 2007 Extensible Markup Language (XML), which is based on
Standard Generalized Markup Language (SGML), features strict syntax
rules and a language -- Document Type Definition (DTD) -- for defining
structural constraints. Learn about XML 1.0 and its Unicode foundation,
as well as all the new features that XML 1.1 offers, and the controversy
surrounding this latest version.
Extensible Markup
Language (XML) 1.0 (Fourth Edition)
[W3C Recommendation] is, of
course, the trunk of the sprawling XML technology tree. It builds on
Unicode
[Unicode Consortium
technical report and ISO standard] to define strict rules for text
format as well as the DTD validation language. The current (fourth)
edition of the specification contains accumulated corrections to the
specification and updates to accommodate more recent versions of
Unicode. It has been widely translated, although
the English version is the only normative one, meaning the only
one that is intended to carry the force of standardization.
XML 1.1
XML 1.1 (Second
Edition)
[in development] is the first revision that changes the
definition of a well-formed XML document. The primary change is
to revise the treatment of characters in the XML specification so that
you always refer to the most recent Unicode version rather than a fixed
one. It also provides for the normalization of characters across Unicode
versions by referencing the
Character Model for the World Wide
Web 1.0: Fundamentals
[W3C Recommendation]. XML 1.1 also adds to
the list of line-end characters, adding NEL, a character used for EOL in
IBM mainframe systems. This change is controversial because some feel
that the modest benefit to mainframe users is not worth such a
fundamental change. There is additional controversy because some
observers find all the changes too modest to introduce all the likely
interoperability problems of an XML version change. There has not been
much adoption of XML 1.1 since its completion in February of 2004.
XML is based on
Standard Generalized Markup Language (SGML)
, defined
in ISO 8879:1986 [ISO Standard]. XML represents a significant
simplification of SGML, and it includes adjustments that make it better
suited to the Web environment.
Resources
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