Many dialects of XML?

David Megginson david at
Sat Nov 13 12:10:47 GMT 1999

"Rick Jelliffe" <ricko at> writes:

> * We now have four kinds of XML: WF, Canonicalized, Valid with DTD, XML
> with namspaces: actually, since they are not mutually exclusive, maybe
> that gives us 8 kinds of XML. 

As I understood it, Canonicalized XML was really defining a mask for
comparing XML documents -- it's not a separate dialect that processors 
are free to support or ignore, so it doesn't belong in the list.

All processors must support well-formed XML, so that's a given for any
possible variant.  Still, that leaves the following four combinations:

  Well-formed + valid
  Well-formed + Namespaces
  Well-formed + valid + Namespaces

Compare this list to

  WebSGML + Architectural Forms
  SGML + Architectural Forms

After all, while many XML-related specs (i.e.Schemas and XSL) require
Namespaces, many SGML-related specs (i.e. HyTime and DSSSL) require
Architectural Forms.

Actually, I'm cheating a little in SGML's favour right now, since the
SGML declaration creates a potentially infinite number of SGML
variants that any SGML parser is free to support or reject (outside
the reference concrete syntax): in SGML you can end up with a
processor that allows UTF-16, 4096-character PIs and 8-character
names, and another that allows only US-ASCII, 128-character PIs, and
1024-character names.

> But there is no standardized way for a document to announce which of
> these forms it is (I suppose the standalone declaration does
> something like this).  

Yes, the SGML declaration helps that situation a little, but only to
the extent that you can find out *why* two SGML tools refuse to

All the best,


David Megginson                 david at

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