Return the searchable regular expressions for the single keyword.

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())