Additional commentary on xsd:any elements.
Rather than encode and decode the XML Schema(s) in the Avro schema, just
provide links to where they came from.

If somebody needs to generate an XML Schema from an Avro schema, they
can add that functionality in later.
Backtracking with xsd:any support.

Stores the element and any stacks to keep track of the current status as
the previous nodes are followed.

Testing required.
Set up to use default value, if any.
Adding support for default & fixed element & attribute values.

Requires testing.