Element Structure for XML (Clause 7)
Despite Michael's request that messages be kept to a single subject within
the list I have decided not to bombard you all with one message per point I
want to make, but have tried to cover questions raised by one of the set of
forms in one posting. This set of points relates to dd-1996-0002-f3.html,
which deals with Element Structure, and also to the points relating to
Processing Instructions in dd-1996-002-f4.html
One way to overcome the differences of how systems handle DocTypes might be
for XML to only allow DTDs to be referenced using a public identifier (that
would be resolved through a catalog), with no local subset, e.g.
<DOCTYPE my-XML PUBLIC "-//The SGML Centre//DTD 12345//EN">
Such a line must be the first declaration in the document instance, but
could be preceded by a comment (or PI) that indicates the public identifier
of the SGML declaration to be used when parsing the document and DTD.
7.4 (a) Empty and unclosed start-tags are obviously not needed by XML, but
could there be a case for NET-enabled start-tags to delimit numeric data?
7.6 (4th bullet)
PIs don't make sense on a network. Their use should be restricted to the
prolog, where they could be useful in setting up the parser (e.g. to
identify a relevant SGML declaration). The thought of allowing a processing
instruction within a document instance that is going to be displayable by
many different plug-ins scares the hell out of me.
A useful restriction might be that the entities referred to can only be data
entities defined using SGML (NDATA "SGML"), or valid SGML subdocuments.
I feel that entities that map to Processing Instructions are not conducive
to portability either. You can only refer to such entities within a document
instance, and I have already made a point about the inamissibility of PIs in
portable document instances.
If PIs are retained then PIC should be changed so that it is not > as this
is required for many processing instructions. (An alternative may be to
allow a character reference to be entered within a PI, but this would make
XML incompatible with SGML.)
Martin Bryan, The SGML Centre, Churchdown, Glos. GL3 2PU, UK
Phone/Fax: +44 1452 714029 WWW home page: http://www.u-net.com/~sgml/