Class Groups

Level	KXP	Effect	Total
1	0	+1 Class Group to a class	(1)
2	5	+1 Class Group to a class	(2)
3	10	+1 Class Group to a class	(3)
4	20	+1 Class Group to a class	(4)
5	40	+1 Class Group to a class	(5)
6	80	+1 Class Group to a class	(6)
7	160	+1 Class Group to a class	(7)
8	320	+1 Class Group to a class	(8)
9	640	+1 Class Group to a class	(9)
10	1200	+1 Class Group to a class	(10)
11	1300	+1 Class Group to a class	(11)
12	1400	+1 Class Group to a class	(12)
13	1500	+1 Class Group to a class	(13)
14	1600	+1 Class Group to a class	(14)
15	1700	+1 Class Group to a class	(15)
16	1800	+1 Class Group to a class	(16)
17	1900	+1 Class Group to a class	(17)
18	2000	+1 Class Group to a class	(18)
19	2100	+1 Class Group to a class	(19)
20	2200	+1 Class Group to a class	(20)
21	2300	+1 Class Group to a class	(21)
22	2400	+1 Class Group to a class	(22)
23	2500	+1 Class Group to a class	(23)
24	2600	+1 Class Group to a class	(24)
25	2700	+1 Class Group to a class	(25)
26	2800	+1 Class Group to a class	(26)
27	2900	+1 Class Group to a class	(27)
28	3000	+1 Class Group to a class	(28)
29	3100	+1 Class Group to a class	(29)
30	3200	+1 Class Group to a class	(30)
31	3300	+1 Class Group to a class	(31)
32	3400	+1 Class Group to a class	(32)
33	3500	+1 Class Group to a class	(33)
34	3600	+1 Class Group to a class	(34)
35	3700	+1 Class Group to a class	(35)
36	3800	+1 Class Group to a class	(36)

Alternate Effect	Alt Total
-1 Class Group to a class	(1)
-1 Class Group to a class	(2)
-1 Class Group to a class	(3)
-1 Class Group to a class	(4)
-1 Class Group to a class	(5)
-1 Class Group to a class	(6)
-1 Class Group to a class	(7)
-1 Class Group to a class	(8)
-1 Class Group to a class	(9)
-1 Class Group to a class	(10)
-1 Class Group to a class	(11)
-1 Class Group to a class	(12)
-1 Class Group to a class	(13)
-1 Class Group to a class	(14)
-1 Class Group to a class	(15)
-1 Class Group to a class	(16)
-1 Class Group to a class	(17)
-1 Class Group to a class	(18)
-1 Class Group to a class	(19)
-1 Class Group to a class	(20)
-1 Class Group to a class	(21)
-1 Class Group to a class	(22)
-1 Class Group to a class	(23)
-1 Class Group to a class	(24)
-1 Class Group to a class	(25)
-1 Class Group to a class	(26)
-1 Class Group to a class	(27)
-1 Class Group to a class	(28)
-1 Class Group to a class	(29)
-1 Class Group to a class	(30)
-1 Class Group to a class	(31)
-1 Class Group to a class	(32)
-1 Class Group to a class	(33)
-1 Class Group to a class	(34)
-1 Class Group to a class	(35)
-1 Class Group to a class	(36)

Each level, pick a class group. You add that group to a class on your character. Ex: you pick custom and add it to your thief1 class. Now it counts as rogue and custom.

For the Alternate version, instead you get remove a group from a class you have. This can leave a class not part of any group.