def concat_rfc_lines(lines):
    """
    Given a list of lines where a same RFC is described on multiple lines, concat
    the lines describing the same RFC.
    """
    rfc_lines = []
    current_rfc = ''
    for line in lines:
        if line.startswith('RFC'):
            rfc_lines.append(current_rfc)  # End of previous RFC, append it to list.
            current_rfc = line  # Get beginning of new rfc.
        else:
            current_rfc += line
    return rfc_lines