XML : XPATH get Entrys with Value 1 on 5. Position of Attribute

I have a XML File:

  <attribute id="1" export="01101">    <value>test</value>  </attribute>    

Now, I want all Entrys, where the Number is 1 on 5th. Digit in Attribute export. I use PHP for the Query. I have tried this, but doesen't work:

  $xpath->query("//attribute/@export[substring(., 4, 1) = '1]");    

Any Ideas? Thank you.