use TagReader;
$xende ="</xref>";
    my $p=new TagReader "testfile.sgm";
    my @tag;
    while(@tag = $p->getbytoken(1)){
            if ($tag[0]=~/xref/i)
        {
            my $mod_xtag = $tag[0].$xende;
            print $mod_xtag;
        }    }