docs: def _get_searchable_regex(basic=None, hidden=None):
      """Return the searchable regular expressions for the single keyword."""
      # Hidden labels are used to store regular expressions.
      basic = basic or []
      hidden = hidden or []
  
      hidden_regex_dict = {}
      for hidden_label in hidden:
          if _is_regex(hidden_label):
              hidden_regex_dict[hidden_label] = \
                  re.compile(
                      current_app.config["CLASSIFIER_WORD_WRAP"]
                      % hidden_label[1:-1]
              )
          else:
              pattern = _get_regex_pattern(hidden_label)
              hidden_regex_dict[hidden_label] = re.compile(
                  current_app.config["CLASSIFIER_WORD_WRAP"] % pattern
              )
  
      # We check if the basic label (preferred or alternative) is matched
      # by a hidden label regex. If yes, discard it.
      regex_dict = {}
      # Create regex for plural forms and add them to the hidden labels.
      for label in basic:
          pattern = _get_regex_pattern(label)
          regex_dict[label] = re.compile(
              current_app.config["CLASSIFIER_WORD_WRAP"] % pattern
          )
  
      # Merge both dictionaries.
      regex_dict.update(hidden_regex_dict)
  
      return list(regex_dict.values())