Re: union operator and predicates in XSLT patterns

On Monday, 24 January 2011 at 6:36PM, Michael Kay wrote:

On 24/01/2011 17:06, HILLMAN, Tomos wrote:

Hi; just a quick query for my own understanding. Apologies if I've gotten the wrong list.

I wanted to use both a union and operator in an XLST template, i.e. match="(div1|div2)[not(@role)]" (simplified).

This is, I think, equivalent in XPath 2.0 as "/*//(div1|div2)[not(@role)]", which I would expect to follow the rule for patterns in XSLT (the node $N matches pattern PAT if $N is a member of expression "root($N)//(PAT)". However, this shows as invalid.

Can someone explain this to me? :)

One of the reasons for the restriction that "|" is allowed only as the
top-level operator in an XSLT pattern is that it affects the algorithm
for computing the default priority of the template rule.

You can write this pattern as

div1[not(@role)] | div2[not(@role)]

or as

*[not(@role)][self::div1 or self::div2]

(In Saxon, the first version will perform better).

Michael Kay
Saxonica

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