In the world of the Internet, support for a feature set has to be ubiquitous or it might as well not be there at all. The big Web browser vendors have made it very clear that they are not going to build full SGML support into their products. They would much rather add proprietary script extensions to HTML and use the complexity of full SGML as an excuse not to support it. XML takes away that excuse and makes support for open, human-readable, extensible markup a reasonable customer requirement.--XML - Questions & Answers