def get_reg_dict(kwd_df):
    """
    Create a dictionary of domains. All regexes belonging to a domain are joined into one regex.

    Parameters
    ----------
    kwd_df: DataFrame
        dataframe with the columns `domain` and `regex`

    Returns
    -------
    dict
        dictionary with the domain as key and a "joined domain regex" as value
    """
    reg_dict = dict()
    for domain in kwd_df.domain.unique():
        reg_dict[domain] = '|'.join(kwd_df.query("domain == @domain").regex)
    return reg_dict