docs: def scan(self, folder, sub=None, next_=None):
          """ Request immediate rescan of a folder, or a specific path within a
          folder.
  
              Args:
                  folder (str): Folder ID.
                  sub (str): Path relative to the folder root. If sub is omitted
                      the entire folder is scanned for changes, otherwise only
                      the given path children are scanned.
                  next_ (int): Delays Syncthing's automated rescan interval for
                      a given amount of seconds.
  
              Returns:
                  str
          """
          if not sub:
              sub = ''
          assert isinstance(sub, string_types)
          assert isinstance(next_, int) or next_ is None
          return self.post('scan', params={'folder': folder,
                                           'sub': sub,
                                           'next': next_})