Re: [xsl] XPath that returns nothing

[David Carlisle <davidc@xxxxxxxxx>]

On 27/09/2011 09:42, Andrew Welch wrote:
> On 26 September 2011 22:17, Olivier Lefevre<lefevrol@xxxxxxxxx>  wrote:
> > What is the best XPath expression that is guaranteed to return nothing?
> > (best in the sense of simplest, always works and costs as little as
> > possible to evaluate). I was hoping it'd be the empty string but that
> > seems forbidden.
>
> Out of interest, why do you ask?

Usual reason for wanting this is as a default value for a parameter so 
you can go

<xsl:param name="x" select="()"/.
...

<xsl:value-of select="$x/a/b"/>

incidentally () is the _only_ expression that is guaranteed to return 
nothing and to be safe in a schema aware xslt2 processor. Other 
expressions that may statically be determined empty may raise an error.

david

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