code: def open_ioc(fn):
          
          parsed_xml = xmlutils.read_xml_no_ns(fn)
          if not parsed_xml:
              raise IOCParseError('Error occured parsing XML')
          root = parsed_xml.getroot()
          metadata_node = root.find('metadata')
          top_level_indicator = get_top_level_indicator_node(root)
          parameters_node = root.find('parameters')
          if parameters_node is None:
              # parameters node is not required by schema; but we add it if it is not present
              parameters_node = ioc_et.make_parameters_node()
              root.append(parameters_node)
          return root, metadata_node, top_level_indicator, parameters_node
docs: Opens an IOC file, or XML string.  Returns the root element, top level
          indicator element, and parameters element.  If the IOC or string fails
          to parse, an IOCParseError is raised.
  
          This is a helper function used by __init__.
  
          :param fn: This is a path to a file to open, or a string containing XML representing an IOC.
          :return: a tuple containing three elementTree Element objects
           The first element, the root, contains the entire IOC itself.
           The second element, the top level OR indicator, allows the user to add
            additional IndicatorItem or Indicator nodes to the IOC easily.
           The third element, the parameters node, allows the user to quickly
            parse the parameters.