def METHOD_NAME(s):
    """Remove the outermost brackets for a model string
    Parameter
    ---------
    s : str
        A model expression (but can be any text).
    Returns
    -------
    cleaned : s
         The outermost () is removed (if there is one).
    Examples
    --------
    >>> clean_bracket('(xsphabs.gal * powlaw1d.pl)')
    'xsphabs.gal * powlaw1d.pl'
    """
    if s.startswith('(') and s.endswith(')'):
        return s[1:-1]
    return s