code: private String pubMedURL(){
  
          if(params.length != 2){
              throw new IllegalArgumentException("Wrong number of Parameters for limit string expression");
          }
  
          final String title = record.getValueByFieldName(params[0]);
          String pubMedId = record.getValueByFieldName(params[1]);
  
          if (pubMedId.isEmpty()){
              return title;
          }
  
          String result = "<a href=" + "http://www.ncbi.nlm.nih.gov/pubmed/"+pubMedId+" target=_blank>"+title+"</a>";
          return result;
      }
docs: Create an anchor with the title and the pubMedId
  In the config file use:
  fieldName="func(PUBMED_URL(title,pubMedID))"