For Builders of SGML DTDs and SGML Declarations

Abstract

Some DTD designers also decide to make changes that affect the SGML declaration, and this chapter is mainly for them. The most common case is fairly simple: increasing length limits such as those on element and attribute names. Many designs do this, including HTML. Some DTDs, especially internationalized ones, use SGML declarations that add to the characters permitted in SGML names. Less common and more prone to raise questions are changes like assigning new strings to delimiters (creating a “variant concrete syntax”). As the questions here reflect, this can be a complex task with subtle side-effects; it is fairly uncommon to do it at all, and extremely uncommon to change more than one or two delimiters. This chapter discusses many of these changes and their effects, as well as a few questions relating to optional SGML features.