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Request for help understanding the XML Recommendation

  • From: "Michael Champion" <Mike.Champion@s...>
  • To: <xml-dev@x...>
  • Date: Fri, 28 Apr 2000 14:36:53 -0400

xml recommendation
[This is posted on behalf of a colleague who's having
trouble posting to the list.  He's a very experienced 
software developer but has had only a short exposure to 
XML.  Thus he's working strictly from the XML Recommendation
itself rather than from what "everybody knows it really
means". Thanks in advance for any assistance you can render.] 

-------------------------------------------------
I'm writing an XML parser, and I seem to have
discovered some odd things in the Spec.

Six of the eighty-nine productions are unreachable
from the start symbol.  In four of the cases that's
OK -- sort of -- because the productions get used in
notes about validity constraints (although, it's at least
a little *odd* to present them as productions...).
One more is explained as a validity constraint in the Errata.

The real problem is that one is *not* used at all, as
far as I can tell.

It is:
  
  [30] extSubset    

Unless I have gone mad  (which possibility must, I
fear, be fairly considered)  this  mysterious
symbol is not only unreachable from the start
symbol -- it is not referenced anywhere at all 
in the XML Spec (1.0) except in the left-hand-
sides of its own definition.

(and, by the way, the other Unreachables are [6] Names, 
[8] Nmtokens,  [33] LanguageID,
[78] extParsedEnt, and [79] extPE.) 

To a country boy like me, this means that the XML 
Spec would have the same meaning if this
production was entirely omitted.  Bob DuCharme's
book "XML the Annotated Specification" pretty much 
just repeats production 30 in English,  and Tim Bray's 
Annotated XML Specification just
says "As you'll see later in the spec, different 
external parsed entities can be in different encodings 
of Unicode, and can have Text Declarations to help 
handle these encodings. Since the external subset 
is (as the spec doesn't make quite clear enough) 
an external parsed entity, it can have one too."

Hmmm.

Surely I must be mistaken.  Can anyone explain this???





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