Just as the W3C is finishing up XHTML 1.0, recasting HTML 4.0 into an XML grammar, ISO has released a Draft International Standard of its version of HTML, building on the W3C's HTML 4.0 recommendation with additional SGML-specific material.

ISO/IEC 15445:1999 goes in some different directions than XHTML. Most obviously, ISO has kept upper-case representations of all the element and attribute names. Case-sensitivity is discussed in particular situations, but otherwise ISO/IEC 15445 makes very few demands regarding case. (Unlike XML, SGML permits case folding.) This version of HTML includes an SGML declaration for use with SGML processors handling HTML, and describes how 'validating HTML systems' should process HTML. Unlike XHTML, it subsets HTML 4.0 rather than preserving all of its contents.

The ISO version of HTML stays out of the multiple DTDs/namespaces issue that confounded XHTML 1.0. While two DOCTYPE declarations are permitted ("ISO/IEC 15445:1999//DTD HyperText Markup Language//EN" and "ISO/IEC 15445:1999//DTD HTML//EN"), they both reference the same DTD. The standard also provides an architectural forms declaration for HTML 4.0, and specifies additional character encoding handling.

Robin Cover's SGML/XML Web Page has additional information on this and other standards efforts related to SGML and XML.