code: public XSDocument startUnion(String... memberParts) throws SAXException{
          xml.startElement(URI_XSD, "union");
  
          StringBuilder buff = new StringBuilder();
          for(int i=0; i<memberParts.length; i+=2){
              if(buff.length()>0)
                  buff.append(' ');
              buff.append(xml.toQName(memberParts[i], memberParts[i+1]));
          }
          if(buff.length()>0)
              xml.addAttribute("memberTypes", buff.toString());
  
          xml.endElement();
          return this;
      }
docs: /*-------------------------------------------------[ Union ]---------------------------------------------------