docs: def start(cls, ev=None):
          """
          Start the query to aleph by ISSN.
          """
          ViewController.log_view.add("Beginning AlephReader request..")
  
          ViewController.issnbox_error.reset()
          issn = ViewController.issn.strip()
  
          # make sure, that `issn` was filled
          if not issn:
              ViewController.issnbox_error.show("ISSN nebylo vyplněno!")
              ViewController.log_view.add("No ISSN! Aborting.")
              return
  
          ViewController.issnbox_error.hide()
          ViewController.issn_progressbar.reset()
          ViewController.issn_progressbar.show(50)
          ViewController.log_view.add("For ISSN `%s`." % issn)
  
          make_request(
              url=join(settings.API_PATH, "aleph/records_by_issn"),
              data={'issn': issn},
              on_complete=cls.on_complete
          )