Serialize an element named name, with the indicated attributes
and value.
if (!(value instanceof Data))
throw new IOException("Can't serialize a " + value.getClass().getName() + " with a DataSerializer.");
Data data = (Data)value;
context.startElement(name, attributes);
context.serialize(new QName("", STRINGMEMBER), null, data.stringMember);
context.serialize(new QName("", FLOATMEMBER), null, data.floatMember);
context.endElement();