docs: def is_valid_size(size, chunk_size):
          """Validate max theoretical size."""
          min_csize = current_app.config['FILES_REST_MULTIPART_CHUNKSIZE_MIN']
          max_size = \
              chunk_size * current_app.config['FILES_REST_MULTIPART_MAX_PARTS']
          return size > min_csize and size <= max_size