Re: [xml] PEReferences - tricky and error-prone

[Daniel Veillard <veillard redhat com>]

On Mon, Jun 03, 2002 at 11:11:14AM +0200, Peter Jacobi wrote:
> Dear All,
>
> While trying to eliminate the last usage of ctxt->token, I had to do
> some experiments with PERefences. As already the W3C REC points
> out, PERefeferences are primary used to author tricky and
> error-prone XML, and so I'm somewhat confused. 
>
> Is the following is valid (current libxml2 votes no, as 
> does XMLSpy 3.5):
>
> t4.xml
> <?xml version='1.0'?>
> <!DOCTYPE root SYSTEM 't4.dtd'>
> <root>&abc;</root>
>
> t4.dtd
> <!ENTITY % percent "&#x25;">
> <!ENTITY %percent; def "ghi">
> <!ENTITY abc "%def;">
> <!ELEMENT root (#PCDATA)>
>
> This example tests, whether it is O.K. to have the
> '%' of an EntitityDecl given by an PEReference.
>
> It is stated in the REC section 2.8
>  
> > The markup declarations may be made up in whole or in part of 
> > the replacement text of parameter entities. The productions later 
> > in this specification for individual nonterminals (elementdecl,
> > AttlistDecl, and so on) describe the declarations after all the 
> > parameter entities have been included.
> >
> > Parameter entity references are recognized anywhere in the 
> > DTD (internal and external subsets and external parameter entities),
> > except in literals, processing instructions, comments, and the
> > contents of ignored conditional sections (see 3.4 Conditional
> >  Sections). They are also recognized in entity value literals. The use 
> > of parameter entities in the internal subset is restricted as described
> > below.
>
> So my reading of these two paragraphs imply, that the '%'
> may be read from an PEReference.
>
> Opinions?

  That sounds objectable because it inter-mixes 2 level. 
What does Xerces, MSXML and XP report about it ?  I could ask the XML Core
working group about this if there isn't a coherent set of results from parsers.
But I would be surprized if this wasn't covered as part of the XML Test suite
from W3C/NIST

Daniel

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