Class Any

object --+    
         |    
     Field --+
             |
            Any

Any text value. This field is tricky. Since any data could be stored in
the field we can't handle all the cases.
The class uses xml.marshal.generic to convert python-ic simple data
structures into xml. By simple we mean any POD. Note that a class derived
from object requires the marshaller to be extended that's why this field
does not accept instance of such classes.
When reading XML we consider node XML text as if it was previously
generated by a xml marshaller facility (xml.marshal.generic.dumps).
If it fails then we consider the data as if it was produced by some other
external source and return False indicating that user Controller should
parse the XML data itself. In such case field value is False.
To access the original XML input two class member variables are populated:
- <field>_xml contains the original XML text
- <field>_dom contains the corresponding XML DOM node

Validate data according to this fields parameters.

@return True if data is ok, otherwise return a string (!) describing
        why the data is invalid.

Note that this method returns either True or an error string, not False!

The Field class considers any data as valid and returns True.