undef $/;
$content = <DATA>;
$content =~s#([^<]*)(<(?:sur|given)name>.*</(?:sur|given)name>)#$1."<authorfield>".&indivauth($2)."</authorfield>"#egi;

sub indivauth
{
	$au{sur} = 'given';
	$au{given} = 'sur';
	($inline) = @_;
	$inline =~s#(<surname>(?:(?!<sur|</au>).)*?</givenname>)#<au>$1</au>#gsi;
	return "$inline";
}
open (FOUT, "> out.txt");
print FOUT $content;