[xsl] Converting a string to a double

["tom tom" <tomxsllist@xxxxxxxxxxx>]

Hi all,

Using the following XML:

<i>
  <b>
     <id>urn:ttt:188589</id>
  </b>
  <b>
     <id>urn:ttt:188689</id>
  </b>
  <b>
     <id>urn:ttt:188989</id>
  </b>
</i>

I want to see if the document contains an id tag with a particular number 
after the string 'ttt:' I can only do this by comparing this value with a 
double datatype value stored in a variable $a. What is the best way to do 
this in XSLT 2?

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