[xslt] XSLT counting elements with a given value

I need to count the number of elements in an XML file that have a particular value (to verify uniqueness). The XML file looks like this:

EDIT: I updated the original "simplified" XML with the actual hairy mess someone designed. Unfortunately, this is going to make all the previous Answers really confusing and wrong unless edited.

<root>
  <ac>
   <Properties>
     <Property Name="Alive">
      <Properties>
        <Property Name="ID">
         <Properties>
           <Property Name="Value">
            <long>11007</long>
           </Property>
         </Properties>
        </Property>
      </Properties>
     </Property>
     <Property Name="Dead">
      <Properties>
        <Property Name="ID">
         <Properties>
           <Property Name="Value">
            <long>11008</long>
           </Property>
         </Properties>
        </Property>
      </Properties>
     </Property>
     ...
     <Property Name="MostlyDeadAllDay">
      <Properties>
        <Property Name="ID">
         <Properties>
           <Property Name="Value">
            <long>99001</long>
           </Property>
         </Properties>
        </Property>
      </Properties>
     </Property>
   </Properties>
  </ac>
</root>

I am trying to define a variable to see how many of the properties at the Alive/Dead level have the long value (ID) as defined in a template parameter. Something along these lines (though I suspect this is wrong)...

<xsl:param name="parPropId"/>
<xsl:variable name="countProperties">
   <xsl:value-of select="count(/root/ac/
      Properties/Property/
      Properties/Property[@Name = 'ID']/
      Properites/Property[@Name = 'Value']/long = $parPropId)"/>
</xsl:variable>

There can be multiple Property elements defined at the "ID" level. But I am fairly certain I can count on just one Property element ("Value") under "ID", and only one "long" element under "Value".

[disclaimer] Whoever designed the overall XML file I'm stuck working with REALLY didn't know how to structure XML (e.g., backwards use of attributes versus elements). I fear my XSLT thinking has temporarily been warped :) as a result. [/disclaimer]

Your xpath is just a little off:

count(//Property/long[text()=$parPropId])

Edit: Cerebrus quite rightly points out that the code in your OP (using the implicit value of a node) is absolutely fine for your purposes. In fact, since it's quite likely you want to work with the "Property" node rather than the "long" node, it's probably superior to ask for //Property[long=$parPropId] than the text() xpath, though you could make a case for the latter on readability grounds.

What can I say, I'm a bit tired today :)

<xsl:variable name="count" select="count(/Property/long = $parPropId)"/>

Un-tested but I think that should work. I'm assuming the Property nodes are direct children of the root node and therefor taking out your descendant selector for peformance