use XML::DOM;
 
 
my $xml =<<EOXML;
<Stuff>
  <Things>
    <Thing />
    <Thing />
  </Things>
  <BadThing />
</Stuff>
EOXML
 
my $parser = new XML::DOM::Parser;
my $doc = $parser->parse($xml);
  
my $things = $doc->getElementsByTagName ("Things")->[0];
  
my $newthing = $doc->createElement('Thing');
$things->appendChild($newthing);
 
my $badthings =  $doc->getElementsByTagName ("BadThing");
 
foreach $badthing ( @{$badthings} )
{
   $doc->getDocumentElement()->removeChild($badthing);
}
 
print $doc->toString();