'a Femtolib.Config_file.wrappers ->
'b Femtolib.Config_file.wrappers ->
'c Femtolib.Config_file.wrappers ->
?group:Femtolib.Config_file.group ->
string list ->
?short_name:string ->
'a * 'b * 'c -> string -> ['a * 'b * 'c] Femtolib.Config_file.cp_custom_type