docs: def render(self, name, value, attrs=None, renderer=None):
          """Include a hidden input to store the serialized upload value."""
          location = getattr(value, '_seralized_location', '')
          if location and not hasattr(value, 'url'):
              value.url = '#'
              if hasattr(self, 'get_template_substitution_values'):
                  # Django 1.8-1.10
                  self.template_with_initial = (
                      '%(initial_text)s: %(initial)s %(clear_template)s'
                      '<br />%(input_text)s: %(input)s')
          attrs = attrs or {}
          attrs.update({'data-upload-url': self.url})
          hidden_name = self.get_hidden_name(name)
          kwargs = {}
          if django_version >= (1, 11):
              kwargs['renderer'] = renderer
  
          parent = super(StickyUploadWidget, self).render(name, value, attrs=attrs, **kwargs)
          hidden = forms.HiddenInput().render(hidden_name, location, **kwargs)
  
          return mark_safe(parent + '\n' + hidden)