XML.com FAQs > A. General questions
Question:  A.7 Why is XML such an important development?

It removes two constraints which were holding back Web developments:

  1. dependence on a single, inflexible document type (HTML);
  2. the complexity of full SGML, whose syntax allows many powerful but hard-to-program options.

XML simplifies the levels of optionality in SGML, and allows the development of user-defined document types on the Web.

This FAQ is from The XML FAQ, maintained by Peter Flynn