Hi, here is:
<?php
$mgr=new XmlManager(null);
$con=$mgr->openContainer("userscontainer.dbxml");
$qc=$mgr->createQueryContext();
$uc=$mgr->createUpdateContext();
$mod=$mgr->createModify();
$select=$mgr->prepare("/users/user[@uname='maria']/name", $qc);
$mod->addUpdateStep($select,"MismoERROR");
$retdoc=$mgr->query("collection('userscontainer.dbxml')/users");
$res=$mod->execute($retdoc,$qc,$uc);
unset($con);
?>
The method it's the "execute" of the Berkeley XML Db PHP API.