options are a list
http://search.cpan.org/grep?release=XML-Simple-2.18&string=AttrIndent&i=1&n=1

1034:# Try the 'AttrIndent' option (assume NoSort defaults to off)
1046:$_ = XMLout($ref, AttrIndent => 1, RootName => 'opt');
1054:', 'AttrIndent seems to work');
[download]