...
XML document from Post payload
In addition to chaining multiple forms with common data sources from XSD together via the Form Action Post as described above, it is also possible to write a servlet or other web code that does a Post request with a form Url to the
Form Server. This request can also be coded to contain an XML document. If the XML document conforms to and is in the same namespace as one of the form's documents (either from-scratch palette controls or from XSD schema datasource), then the Form Server will use that XML document to initialize the form's fields.
...