Shouldn't we be distinguishing between the SGML declaration, which
describes a particular document or class of documents, and the
system declaration, which describes the capabilities of a particular
application?
To quote from the SGML Handbook, p. 487, just preceding the text of
ISO 8879, clause 15.6 System Declaration:
"A system declaration is the complement of an SGML declaration.
While an SGML declaration identifies the features that a parser
requires in order to deal with a particular document, the system
declaration identifies the set of SGML declarations that a system
can deal with."
And, from clause 15.3.2 Conformance to System Declaraion:
"A conforming SGML system shall be capable of processing any
conforming SGML document that is not inconsistent with the
system's system declaration (see 15.6).
Note - As this International Standard does not define data content nota-
tions or system data, a system's inability to process such text does not
affect whether it is a conforming SGML system."
I think that the RFC should call out:
1. an assumed SGML declaration
2. a System declaration which must be minimally supported
The issue then is whether and how to allow other SGML declarations.
If an alternate SGML declaration is permitted, then it should be
communicated with the HTML document entity.
Glenn