docs: def filter_metadata(metadata, user_filter, default_filter):
      """Filter the cell or notebook metadata, according to the user preference"""
      actual_keys = set(metadata.keys())
      keep_keys = apply_metadata_filters(user_filter, default_filter, actual_keys)
  
      for key in actual_keys:
          if key not in keep_keys:
              metadata.pop(key)
  
      return metadata