XML::XML2JSON is a Perl module to convert XML to JSON (and JSON to XML) using
the following rules from Google (http://code.google.com/apis/gdata/json.html):

Basic:
- The feed is represented as a JSON object; each nested element or attribute
  is represented as a name/value property of the object.
- Attributes are converted to String properties.
- Child elements are converted to Object properties.
- Elements that may appear more than once are converted to Array properties.
- Text values of tags are converted to $t properties.

Namespace:
- If an element has a namespace alias, the alias and element are concatenated
  using "$". For example, ns:element becomes ns$element.

XML:
- XML version and encoding attributes are converted to version and encoding
  attributes of the root element, respectively.