code: protected Map<String, Object> getSignableData()
      {
      	final Map<String, Object> doc = getSendableData();
  
      	// remove node-specific data
      	for (int i = 0; i < excludedFields.length; i++) {
      		doc.remove(excludedFields[i]);
      	}
          return doc;
      }
docs: Builds and returns a map of the envelope data, suitable for signing with the included signer
  
  @return map of envelope data, suitable for signing