If you looked at the documentation onXML::Simple, you probably saw that this module is deprecated:

You really don't want to use this module in new code.

And:

The use of this module in new code is discouraged. Other modules are available which provide more straightforward and consistent interfaces. In particular, XML::LibXML is highly recommended and XML::Twig is an excellent alternative.

And:

The major problems with this module are the large number of options (some of which have unfortunate defaults) and the arbitrary ways in which these options interact - often producing unexpected results.

If you search this forum, you'll find a number of posts explaining why you should not use this module (at least not for new code).