code: def header(parent, identifier, datestamp, sets=None, deleted=False):
      
      e_header = SubElement(parent, etree.QName(NS_OAIPMH, 'header'))
      if deleted:
          e_header.set('status', 'deleted')
      e_identifier = SubElement(e_header, etree.QName(NS_OAIPMH, 'identifier'))
      e_identifier.text = identifier
      e_datestamp = SubElement(e_header, etree.QName(NS_OAIPMH, 'datestamp'))
      e_datestamp.text = datetime_to_datestamp(datestamp)
      for spec in sets or []:
          e = SubElement(e_header, etree.QName(NS_OAIPMH, 'setSpec'))
          e.text = spec
      return e_header
docs: Attach ``<header/>`` element to a parent.