docs: def stash(self, storage, url):
          """Stores the uploaded file in a temporary storage location."""
          result = {}
          if self.is_valid():
              upload = self.cleaned_data['upload']
              name = storage.save(upload.name, upload)
              result['filename'] = os.path.basename(name)
              try:
                  result['url'] = storage.url(name)
              except NotImplementedError:
                  result['url'] = None
              result['stored'] = serialize_upload(name, storage, url)
          return result