In his essay "A Technical Introduction to XML"
[http://www.xml.com/pub/a/98/10/guide0.html] Norman Walsh writes:
"This is not to say that XML can be expected to completely replace SGML. While XML is being designed to deliver structured content over the web, some of the very features it lacks to make this practical, make SGML a more satisfactory solution for the creation and long-time storage of complex documents. In many organizations, filtering SGML to XML will be the standard procedure for web delivery".
Could anyone please elaborate on what exactly these features are, and why, if the statement is correct, SGML is "a more satisfactory solution for the creation and long-time storage of complex documents".