code: def error(errors):
      
      e_tree, e_oaipmh = envelope()
      for code, message in errors:
          e_error = SubElement(e_oaipmh, etree.QName(NS_OAIPMH, 'error'))
          e_error.set('code', code)
          e_error.text = message
      return e_tree
docs: Create error element.