Caveats

       Some care is required in creating data structures which
       will be passed to "XMLout()".  Hash keys from the data
       structure will be encoded as either XML element names or
       attribute names.  Therefore, you should use hash key names
       which conform to the relatively strict XML naming rules:

       Names in XML must begin with a letter.  The remaining
       characters may be letters, digits, hyphens (-), under-
       scores (_) or full stops (.).  It is also allowable to
       include one colon (:) in an element name but this should
       only be used when working with namespaces - a facility
       well beyond the scope of XML::Simple.

       You can use other punctuation characters in hash values
       (just not in hash keys) however XML::Simple does not sup-
       port dumping binary data.

       If you break these rules, the current implementation of
       "XMLout()" will simply emit non-compliant XML which will
       be rejected if you try to read it back in.  (A later ver-
       sion of XML::Simple might take a more proactive approach).
[download]

-- Randal L. Schwartz, Perl hacker