def _is_sld(model_info, par):
    """
    Return True if parameter is a magnetic magnitude or SLD parameter.
    """
    if par.startswith('M0:'):
        return True
    if '_pd' in par or '.' in par:
        return False
    for p in model_info.parameters.call_parameters:
        if p.id == par:
            return p.type == 'sld'
    for p in model_info.parameters.kernel_parameters:
        if p.id == par:
            return p.type == 'sld'
    return False
