code: @Override
    protected void marshallElementContent(XMLObject xmlObject, Element domElement) throws MarshallingException {
  
      // Find out if the our namespace already has been defined, and if so, get the prefix.
      //
      final String namespace = CurrentAddressType.TYPE_NAME.getNamespaceURI();
      Optional<String> _prefix = xmlObject.getNamespaceManager()
        .getNamespaces()
        .stream()
        .filter(n -> namespace.equals(n.getNamespaceURI()))
        .map(n -> n.getNamespacePrefix())
        .findFirst();
      String prefix = _prefix.isPresent() ? _prefix.get() : CurrentAddressType.TYPE_NAME.getPrefix();
      
      StringBuilder sb = new StringBuilder();
  
      final List<XMLObject> childXMLObjects = xmlObject.getOrderedChildren();
      if (childXMLObjects != null && childXMLObjects.size() > 0) {
        for (final XMLObject childXMLObject : childXMLObjects) {
          if (childXMLObject == null) {
            continue;
          }
          if (!(childXMLObject instanceof XSString)) {
            throw new MarshallingException("Unexpected type of child element - " + childXMLObject.getClass().getName());
          }
          XSString childString = (XSString) childXMLObject;
          if (childString.getValue() == null) {
            continue;
          }
          String localPart = childString.getElementQName().getLocalPart();
          sb.append(String.format("<%s:%s>%s</%s:%s>", prefix, localPart, childString.getValue(), prefix, localPart));
        }
      }
      if (sb.length() > 0) {
        byte[] bytes;
        try {
          bytes = sb.toString().getBytes("UTF-8");
        }
        catch (UnsupportedEncodingException e) {
          throw new MarshallingException(e);
        }
        String base64String = Base64Support.encode(bytes, true);
        ElementSupport.appendTextContent(domElement, base64String);
      }
    }
docs: The element content of a {@code CurrentAddressType} is the Base64-encoding of the serialized value of the
  {@code CurrentAddressStructuredType}. So ... we have to get there by iterating over our child elements.