xml - XML パブリッシャーの列の合計

Question

使用して合計を計算するRTF TEMPLATEで取得している列があります-<?sum(current-group()/PAYMENT[../PAYMENT != ''])?>

***Tax deduction*** 
Description                        current                                              YTD
Voluntary                 `<?sum(current-group()/PAYMENT[../PAYMENT != ''])?>`        `<?sum(current-group()/YEAR)?`>
Involuntary               <?PAYMENT?>                                                 `<?sum(current-group()/YEAR)?`>
Pre tax                   `<?sum(current-group()/PAYMENT[../PAYMENT != ''])?>`        `<?sum(current-group()/YEAR)?`>

current値とYTD列の値の合計を計算したい。どうやってやるの？