Features and Rules of ISO 8879

A Summary for Use

In Discussions of the W3C SGML Working Group

And Editorial Review Board

Document W3C-SGML-ERB DD-1996-0002

C. M. Sperberg-McQueen

12 September 1996

Table of Contents

This document summarizes some of the salient features of ISO 8879 which may or may not require revision in XML. The `features' included here are not limited to those called features by the standard; they include other characteristics and rules as well.

In virtually all cases, the inclusion of an item in these lists may be interpreted as a suggestion that the W3C SGML Working Group and Editorial Review Board will need to decide explicitly whether XML should (a) work exactly the same way as SGML, (b) work in only one of the ways allowed by SGML, (c) provide the same functionality in some other way, or (d) suppress the feature / functionality in question. That is, after each statement, the question "Should this be true in XML as well?" may be understood implicitly, even if not explicit.

In some cases, an entry is present only as a reminder of some SGML construct which the compiler or others have found hard to follow or obscurely expressed in ISO 8879, and which should be described more clearly in XML documentation.

In addition to mentioning some SGML features and rules, the lists below indicate whether those features or rules are omitted or modified by various proposals for subsets or simplifications of SGML. The proposals thus summarized are:

Except as noted, entries have not been reviewed by the authors of the proposals, and so may be in error. Some of these schemes also include proposals that do not fit readily into the format of this list, and are not described here. For full and authoritative information, the documenation for each proposal should be consulted.

Other schemes may be added if we learn of them and they seem to be of interest.

In summarizing the schemes, the following abbreviations are used:

If no note is present, it normally means all the schemes collated to date agree with 8879. In isolated cases, it may mean the compiler just skipped over the item due to inattention, boredom, or a conviction that a note was not necessary. Notes are not normally given for quantity definitions, because few of the schemes collated propose changes to the default or minimum quantities; most either leave the quantities as they are, or propose ignoring or dropping them entirely.

For example, consider the following entry:

This means (1) that minimized end-tags are defined in clause 7.5, and (2) that in basic SGML, all three forms of minimized end-tags are legal and may be used as described in 8879, while none may be used in MGML or minimal SGML, and only one in PSGML. When more than one item is derived from a clause, a letter is attached to the clause number to keep the items distinct; it is not part of the formal clause numbering of ISO 8879.