HTML SpecificationsThe Standard Generalized Markup Language (SGML) is a extensible document language that portably describes embedded data and document structure. It does not define document formating - leaving it up to a viewer to define the appearance of the document. SGML documents require a Document Type Definition (DTD) to define parsing and handling of document structure.
The Hyper-Text Markup Language (HTML) is designed to be an SGML implementation that provides a certain amount for formatting information (Bold, Italic, Font color/size, etc.). In practice, HTML documents are rarely SGML-compliant.
HTML ReferencesGrafman's HTML Tips
World Wide Web Consortium
Hyper-Text Markup Language (HTML) Charter Group
HTML Working Group
SGML Open Consortium
Soft Quad's SGML Resource
Netscape's Web "Standards"