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RE: [xsl] xslt 2, forward compatibility mode.


Subject: RE: [xsl] xslt 2, forward compatibility mode.
From: "Michael Kay" <mhk@xxxxxxxxx>
Date: Tue, 4 Mar 2003 23:48:16 -0000

> 
> <quote>An element enables forwards-compatible behavior for 
> itself, its attributes, its descendants and their attributes 
> if it has an [xsl:]version attribute (see 3.3 Standard 
> Attributes) whose value is greater than 2.0.</quote>
> 
> I'm having a problem with this. 
> If I write a stylesheet with version="15.0" as an attribute 
> of the root element, just what am I saying?

This text is essentially unchanged from the 1.0 spec. It's actually a
brilliant bit of future-proofing.

Suppose that XSLT 3.0 has just been published, and it includes a new
<xsl:perform-magic> instruction, which is implemented in Saxon version
19.2, but not yet in MSXML6. You want to invoke this instruction when
your stylesheet is running under Saxon, but when running under MSXML6,
you just want to leave out that part of the output. So you write:

<xsl:template match="thing" version="3.0">
  <xsl:perform-magic select="magic-dust">
    <xsl:fallback>Sorry, Microsoft don't do magic</xsl:fallback>
  </xsl:perform-magic>
</xsl:template>

Specifying version="3.0" means that the Microsoft processor (or any XSLT
1.0 or 2.0 processor) is obliged to execute the xsl:fallback
instruction. If you had said version="1.0" or version="2.0", then the
processor would instead have thrown a static error saying that there is
no such instruction as xsl:perform-magic.

Michael Kay

> 
> That I hope it will work for the next 13 versions?
> 
> That I don't want any errors reporting?
> 
> Some sort of future proofing?
> 
> Is this unique to xslt? I can't recall it being used on any 
> other recs.
> 
> Does it make sense to anyone else please?
> 
> 
> Regards DaveP.
> 
> **** snip here *****
> 
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