Special Edition Using XSLT

HTML

Technically speaking, HTML is an SGML (Standard Generalized Markup Language) document type. SGML is the father of XML. When the creators of XML designed the markup language, they based it on SGML. In fact, XML is an SGML subset, meaning that markup created in XML should parse correctly in an SGML parser.

XML documents are implicitly SGML documents because XML is a subset. However, that doesn’t mean SGML documents parse successfully using an XML parser. This poses problems when combining HTML and XML technologies. The basic problem involves XML’s rules for well-formedness.

For example, SGML enables you to create elements that have an opening tag but no closing tag. Tim Berners-Lee used this feature of SGML in creating HTML. For example, ...