FrameMaker, from Adobe (See www.adobe.com) is a professional DTP package that is also SGML/XML aware. FrameMaker is also a vital component of the professional batch-pagination Miramo product.

Neil Bradley wrote all of his books in FrameMaker+SGML, and thereby typeset his own books for Addison Wesley (the SGML capabilities are now built-in to the mainstream FrameMaker product).