ALLIED FORMATIONS
Formations do not count as your army’s Allied Detachment, even if they are made up of unitsfrom a different codex to your Primary Detachment, and they do not stop you from taking an
Allied Detachment in the same army. However, the Levels of Alliance rules from the
Warhammer 40,000 rulebook do apply to them and units chosen from a different codex that
are in the same army.
For example, if you included an Ork Formation in the same army as a Primary Detachment
from Codex: Space Marines, then the units from the two Detachments would treat each other
as desperate allies. However, the Ork Formation would not stop you taking an Allied
Detachment in the same army