Integration

I am trying to use the XPATH expression builder to iterate thru a array of strings and concatenate them into one single string field. I have top level element called "counter" which has a array of element "approvers" which in turn contains the string approver. I need to concatenate all the approvers in to one field. I am able to get the count by using

count(bpmn:getDataObject('counter')/approvers)


I do not know how to write the looping logic to iterate thru the array and pick out the string value for each of the index. Can some one please help me or point to any tutorials.