validation of the len of the multi in a group

tiramisu/setting.py

@@ -21,6 +21,12 @@
 # the whole pypy projet is under MIT licence
 # ____________________________________________________________
 
+# available group_type values
+_group_name = ('default', 'family', 'group')
+groups_has_master = ('group', )
+class Group(str): pass
+group_types = tuple(Group(i) for i in _group_name)
+
 class Setting():
     "``Config()``'s configuration options"
     # properties attribute: the name of a property enables this property