Firstly, they aren't called node set fragments, they are called result tree
fragments. Not a pretty name, and the abbreviation RTF is unfortunate, but
we have to live with it.

When the body of an <xsl:variable> element is evaluated (or "instantiated"
to use the correct jargon), the result is written to an RTF. There are only
three things you can do with an RTF: you can use xsl:copy-of to copy it to
the result tree (or to another RTF), you can convert it implicitly or
explicitly to a string, and you can pass it to a function. There aren't any
standard functions that process RTFs, so in practice this means an extension
function.

SAXON and xt both provide extension functions to convert an RTF to a
node-set. This conversion can't be done implicitly. The reason your
xsl:for-each fails is that the expression in the select attribute must yield
a node-set. Nothing else will do, in particular, it cannot be an RTF.

With your <xsl:for-each> commented out, the SAXON message output is what I
would expect; I can't comment on the xt output.

Step back: what is the problem you are trying to solve?

Mike Kay


> -----Original Message-----
> From: Mark D. Anderson [mailto:mda@xxxxxxxxxxxxxx]
> Sent: 14 December 1999 04:14
> To: xsl-list@xxxxxxxxxxxxxxxx
> Subject: what are node set fragments and why are they ruining my life?
> 
> 
> see the minimal xsl and xml file below.
> 
> first off, nothing i've read in the spec or the various xsl tutorials
> make any sense in defining what a node set fragment is.
> they talk about things like "not being well-formed", but (a) i'm not
> clear how one is able to produce something that isn't well-formed,
> and (b) that doesn't match experience as this example shows.
> 
> here i've shown where the mere act of passing a node set (fragment)
> through a call-template is enough to defile it.
> 
> here are the various outputs.
> 
> 1. comment out first for-each, use xt
> output is:
> member 1
> 
> note that there is a result, but no xsl:message instructions are run
> 
> 2. comment out first for-each, use saxon
> output is:
> member local-name=member, id=1
> member local-name=member, id=2
> 
> note that there is no result, but the xsl:message instructions are run
> 
> 3. leave in first for-each, use xt
> output is:
> cannot convert to node-set
> 
> 4. leave in first for-each, use saxon
> member local-name=member, id=1
> member local-name=member, id=2
> Error during source document processing
> At xsl:for-each on line 32 of 
> file:/d:/mda/projects/xmlhacks/xmlidl/test1.xsl: Cannot 
> convert value [** RESULT TREE FRAGMENT **] to
> a node-set
> 
> Thanks to anyone who can elucide this matter.
> 
> -mda
> 
> test1.xml
> 
> <root>
>   <member id="1">member 1</member>
>   <member id="2">member 2</member>
> </root>
> 
> 
> test1.xsl
> 
> <?xml version="1.0" ?>
> 
> <xsl:stylesheet
>   version="1.0"
>   xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
>   xmlns:date="http://www.jclark.com/xt/java/java.util.Date"
>   xmlns:xt="http://www.jclark.com/xt"
>   xmlns:sxf="/com.icl.saxon.functions.Extensions"
>   extension-element-prefixes="date xt sxf"
>   exclude-result-prefixes="date sxf xt"
>   >
>   <xsl:output
>      method="html"
>      indent="yes"
>      doctype-public="-//W3C//DTD HTML 4.0 Transitional//EN"
>   />
>   <xsl:strip-space elements="*"/>
> 
>   <xsl:template match="root">
>     <xsl:variable name="members">
>       <xsl:call-template name="get_members"/>
>     </xsl:variable>
>     <!-- why can't i use a variable? something about result 
> tree fragments... -->
> 
>     <!-- comment this for-each out to avoid the runtime error
>     <xsl:for-each select="$members">
>       <xsl:message>member local-name=<xsl:value-of 
> select="local-name(.)"/>, id=<xsl:value-of 
> select="@id"/></xsl:message>
>     </xsl:for-each>
>     -->
>     <xsl:value-of select="$members"/>
>   </xsl:template>
> 
>   <xsl:template name="get_members">
>     <xsl:variable name="result" select="*"/>
>     <xsl:for-each select="$result">
>       <xsl:message>member local-name=<xsl:value-of 
> select="local-name(.)"/>, id=<xsl:value-of 
> select="@id"/></xsl:message>
>     </xsl:for-each>
>     <!-- same thing as: <xsl:value-of select="$result"/> -->
>     <xsl:value-of select="*"/>
>   </xsl:template>
> 
> </xsl:stylesheet>
> 
> 
> 
>  XSL-List info and archive:  http://www.mulberrytech.com/xsl/xsl-list
> 


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