DuCharme has targeted programmers with moderate to extensive experience with SGML in this user guide/tutorial describing some of the most useful free SGML processing software you'll find anywhere.
Before you read this book, you should either take a class on SGML syntax or read a book on SGML syntax and tutor yourself.
Each chapter covers important parts of an SGML system, including authoring of SGML documents, validation of documents, production of formatted output, and application development tools.
Editing SGML documents with the Emacs text editor": DuCharme describes how to use Emacs, a highly customizable text editor you can configure to help edit SGML documents.
Parsing and validating SGML documents with nsgmls": The nsgmls program validates SGML documents against their DTDs and transforms SGML documents into a form that other programs can more easily process.