<input name="/xy[1]/ab[2]" ... don't need array !!

Hi all
 
 I want to name my POST variables like:
 
 <input name="/ab[1]/cd[2]/ds" value="test">
 
 The NAME is an XPATH (w3c standard).
 
 Using PHP5 xml query I can make some nice things -
 but PHP interprets the NAME as an ARRAY.
 
 while(list($pkey, $pvalue)=each($_POST)) {
 $theElement=$xpath->query($pkey)->item(0); //ERRRRORRR
 ...
 } //not working - $pkey is an ARRAY
 
 How can I set the TYPE of $pkey to STRING ???
 
 This is realy importent and I need a solution at monday.
 
 thanks a lot
 
 Bernhard