Re: [xml] Processing Instructions

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From: Mathias Hasselmann (Mathias.Hasselmann@gmx.de)
Date: Wed Dec 22 1999 - 08:53:49 EST

Daniel Veillard wrote:
>
> > That's a problem for XSLT parsers: XML document with embedded
> > stylesheets have
> > to start with:
> >
> > <?xml-stylesheet type="text/xml" href="#style1"?>
>
> Hum strange, I wasn't actually able to reproduce the problem:
> ~/XML -> cat pi3.xml
> <?xml version="1.0"?>
> <?xml-stylesheet type="text/xml" href="#style1"?>
> <doc/>
> ~/XML -> ./tester pi3.xml
> <?xml version="1.0"?>
> <?xml-stylesheet type="text/xml" href="#style1"?>
> <doc/>
>
> But I commited a fix checking for a list of predefined PI starting
> with "xml", and verified it only genmerates a warning and don't break
> further processing:
>
> ~/XML -> cat pi4.xml
> <?xml version="1.0"?>
> <?xml-unknown type="text/xml" href="#style1"?>
> <doc/>
> ~/XML -> ./tester pi4.xml
> pi4.xml:2: warning: xmlParsePItarget: invalid name prefix 'xml'
> <?xml-unknown type="text/xml" href="#style1"?>
> ^
> <?xml version="1.0"?>
> <?xml-unknown type="text/xml" href="#style1"?>
> <doc/>
> ~/XML ->
>
> It's commited in the CVS bases

The problem occurs if you take the example for embedded stylesheets
from REC-xslt-19991116 (chapter 2.7):

»»» cut »»»

<?xml-stylesheet type="text/xml" href="#style1"?>
<!DOCTYPE doc SYSTEM "doc.dtd">
<doc>
<head>
<xsl:stylesheet id="style1"
                version="1.0"
                xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:fo="http://www.w3.org/1999/XSL/Format">
<xsl:import href="doc.xsl"/>
<xsl:template match="id('foo')">
  <fo:block font-weight="bold"><xsl:apply-templates/></fo:block>
</xsl:template>
<xsl:template match="xsl:stylesheet">
  <!-- ignore -->
</xsl:template>
</xsl:stylesheet>
</head>
<body>
<para id="foo">
...
</para>
</body>
</doc>

««« cut «««

This not nice, but well formed.
James Clark says (in REC-xslt-19991116) something like "This is XML".

So let's ask REC-xml-19980210 about it:

»»» cut »»»

2.8 Prolog and Document Type Declaration

XML documents may, and should, begin with an XML declaration which
specifies the version of XML being used. For example, the following
is a complete XML document, well-formed but not valid:

<?xml version="1.0"?>
<greeting>Hello, world!</greeting>

and so is this:

<greeting>Hello, world!</greeting>

...

Prolog

[22] prolog ::= XMLDecl? Misc* (doctypedecl Misc*)?
[23] XMLDecl ::= '<?xml' VersionInfo EncodingDecl? SDDecl? S? '?>

...

««« cut «««

You see this 'ugly' question mark behind »XMLDecl«?

So this means:
  * If you read <?xml version="1.0"?> in the prolog that's
    fine, because you known to parse a document meant to be
    compilant to version 1.0 of XML.

  * If you read <?xml version="somewhat else"?> you have
    to enable the "somewhat else" parsing mode and if you
    do not know it, you can:
       refuse the document
    or
       inform the user, that you assume that this document
       is compatible to XML version 1.0...

  * If you never read the xml processing instruction you
    are in a similar situation as above. But this time
    you have to use the assumtion, that the document
    could be compilant to version 1.0...

Ciao,
Mathias 

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