An extract from Inquisitor Czevak's tretise about the Eldar, Teachings on the Unholy.
On occasion, servants of the Almighty Emperor may be fortunate or skilled enough to capture an Eldar alive. The majority of those who fall into our hands are from that caste known by our military forces as the Rangers. These Rangers can provide us with much information about their people, under correct inducements. Over the last two millennia, a surprising proportion of these captured Rangers hailed from the craftworld of Alaitoc.
Perplexed by this course of events, my predecessors began a detailed analysis of this craftworld which I have attempted to continue. This has been a very hard task, as Alaitoc is one of the most secretive craftworlds, drifting on the very edge of the galaxy. Ever since war broke out between them and the Emperor's righteous armies, following the Beelze Conflict, they have shunned all direct contact with other races.
Intrigued by the propensity for the Alaitoc Eldar to follow the so-called 'Path of the Outcast' I endeavoured to find the root of this from amongst their number. The information I managed to elicit was interesting but unfortunately the subject died before it could reveal anything of depth or detail.
It appears that the Eldar of Alaitoc are the most puritanical adherents to the culture known as the Path of the Eldar - that lifestyle by which an Eldar will dedicate itself to the pursuit of knowledge in one sphere of life at a time. This zealous attitude has led to many of the Alaitoc Eldar becoming Rangers - either made outcasts by their masters for some slight misdeed, or tiring of the harsh discipline of their craftworld. For some, the very isolation which the Alaitoc Eldar value has only served to heighten their curiousity and inquisitiveness regarding the greater galaxy.
Although disenchanted with their craftworld, those on the Path of the Outcast still remain loyal to Alaitoc and many of them return to it in due course. Due to its isolation, the craftworld makes much use of its many Rangers to gather news, keeping it informed of the actions of other craftworlds and alien races so that the Alaitoc Eldar might respond if necessary.
When the Alaitoc fight a war, they gather their many Rangers through the webway, sending them ahead of their main force to sow disruption and anarchy in their enemy's army. The Rangers are highly skilled at destroying supply dumps and ammo caches, pinning down units trying to attack and generally breaking apart any coordination and cohesiveness the enemy army might have. When the Alaitoc make their major attack, the enemy will already be half-defeated - having spent days or even weeks chasing shadows, they will be desperately trying to gather together the fragments of their army into a fighting force.
Inquisitor Czevak - Teachings on the Unholy, Chapter XI 'The Tyranny of Alaitoc'