RE: [xsl] position()

[Wendell Piez <wapiez at mulberrytech dot com>]

Hi Richard,

At 03:54 PM 4/2/01, you wrote [quoting David]:

> > If you don't want that, then use select="*" just to select elements.

Or of course select="*|text()" for elements that contain text nodes.

> >
> > Or use xsl:number rather than position()
> >
> > David
> >
>Well yes, but I would have thought that xsl like
>
><xsl:template match="object">
>         <xsl:value-of select="concat(position(),' ',@name)"/>
></xsl:template>
>
>on input of
>
><objects>
>         <!-- hello -->
>         <object name="first"/>
>         <object name="second"/>
>         <!-- hello -->
>         <object name="third"/>
>         <object name="fourth"/>
></objects>
>
>Would produce
>
>1 first
>2 second
>3 third
>4 fourth
>
>and not
>
>2 first
>3 second
>5 third
>6 fourth
>
>which seems to be the case.

Your expectation makes sense, but on balance it's best that the spec simply 
count comments rather than provide some complex logic -- even harder to 
understand -- to avoid them. XSLT could have left comments out of the 
source tree altogether. But they decided to let you work with the comments 
if you wanted: probably to support identity transforms and their variants, 
when necessary. As long as they're in the tree, it's better to expect you 
to reckon with them than have some fancy logic to see them sometimes but 
not others, which we'd all have to learn and complain about. This would 
make XPath much nastier than it is.

Whitespace-only text nodes make it bad enough already! :-) Note that even 
the result

>2 first
>3 second
>5 third
>6 fourth

is incorrect for the input you gave. Where'd the whitespace nodes go? This 
is an MS bug, I believe (can someone confirm?). The correct sequence should 
be 4, 6, 10, 12.

In any case, as David said a template

<xsl:template match="objects">
   <xsl:apply-templates select="*"/>
</xsl:template>

or even

<xsl:template match="*[not(text())]" priority="-1">
   <xsl:apply-templates select="*"/>
</xsl:template>

would solve this problem and get you 1, 2, 3, 4 as you expect.

Maybe some future version of XSLT could include an <xsl:strip-comments> 
(and <xsl:strip-processing-instructions>) analogue to <xsl:strip-space> to 
help deal with this situation. But there's no substitute for knowing what 
the source tree looks like and how XPath sees it.

>Also on a related point how can I output the preceding node if and
>only if it is a comment.

Try <xsl:copy-of select="preceding-sibling::node()[1][self::comment()]"/> 
(or xsl:value-of or whatever).

Good luck,
Wendell

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Wendell Piez                            mailto:wapiez@mulberrytech.com
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