Getting "count: Parameter must be a NodeSet" trying to count nodes with a specific numeric value

I'开发者_C百科m using Perl's XML::XPath package in a small script. I'm pretty sure I have an xpath problem, not something specific to that package.

My test data is the following:

<stuff>
 <things>
  <thing>
   <widgets>
    <widget>
     <junk>
      <value>0</value>
     </junk>
    </widget>
    <widget>
     <junk>
      <value>9.0</value>
     </junk>
    </widget>
   </widgets>
  </thing>
 </things>
</stuff>

The expression I'm using is:

//thing[count(number(widgets/widget/junk/value/text())=0)=0]

When I run this, it fails with "count: Parameter must be a NodeSet".

the following code within the count() returns a boolean which is not a node:

number(widgets/widget/junk/value/text())=0

This is not allowed in XPath 1.0

If you want to select <thing/> elements containing no <value/> element with value 0 you can use:

//thing[not(
    widgets/widget/junk/value[number(text())=0]
  )]