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

["Christopher R. Maden" <crism maden org>]

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At 06:50 3/6/02, Peter Jacobi wrote:
> Given that the original example is valid,

I had actually assumed that the original one was invalid, but I was wrong; 
if is valid SGML and isn't ruled out by anything in the XML Recommendation, 
then it's usually a good bet that it is intentionally correct XML (as 
opposed to one of those places where we all took SGML knowledge for granted).

> I assume
> the following one is also valid, due to the automatic
> insertion of blanks around the replacement text:
>
> <!ENTITY % percent "&#x25;">
> <!ENTITY%percent;def "ghi">
> <!ENTITY abc "%def;">
> <!ELEMENT root (#PCDATA)>

Ick - this seems to be one of those places.  The space-adding rule is not 
part of SGML, and so that would absolutely not be valid SGML.  The 
space-adding rule was intended to simplify things by making sure that the 
PEs were always complete tokens (avoiding things like:

<!ENTITY % foo "foo">
<!ENTITY % bar "bar">
<!ELEMENT %foo;%bar; (#PCDATA)>

) but as usual, it appears to have had unintended consequences.  My feeling 
for now is that a parser should accept your example, but if at all 
possible, issue a *very* strong warning, because it seems likely to be made 
illegal in an erratum.

> And I assume, that unescaped use of the
> percent sign (as seen in Matthias' SGML
> example) is not valid XML:
>
> <!ENTITY % percent "%">
> <!ENTITY %percent; def "ghi">
> <!ENTITY abc "%def;">
> <!ELEMENT root (#PCDATA)>

No, it wouldn't be valid XML.  It's valid SGML because of the baroque 
delimiter-in-context rules which mean that % isn't a pero unless followed 
by a name start character.

~Chris, feeling unclean now
- -- 
Christopher R. Maden, Principal Consultant, crism consulting
DTDs/schemas - conversion - ebooks - publishing - Web - B2B - training
<URL: http://crism.maden.org/consulting/ >
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