code: def _add_namespace(marc_xml):
      
      dom = marc_xml
  
      if isinstance(dom, basestring):
          dom = dhtmlparser.parseString(marc_xml)
  
      root = dom.find("root")
      if root:
          root[0].params = {}
  
      for record in dom.find("record"):
          record.params = {}
  
      collections = dom.find("collection")
      if not collections:
          record = dom.find("record")[0]
          return XML_TEMPLATE.replace("$CONTENT", str(record))
  
      for col in collections:
          col.params["xmlns"] = "http://www.loc.gov/MARC21/slim"
          col.params["xmlns:xsi"] = "http://www.w3.org/2001/XMLSchema-instance"
          col.params["xsi:schemaLocation"] = "http://www.loc.gov/MARC21/slim " + \
                     "http://www.loc.gov/standards/marcxml/schema/MARC21slim.xsd"
  
      return str(dom)
docs: Add proper XML namespace to the `marc_xml` record.
  
      Args:
          marc_xml (str): String representation of the XML record.
  
      Returns:
          str: XML with namespace.