Question on npc spell casting lists in DB?

[ChaosSlayer]

I am looking over npc spell lists and trying to figure few thigns out:

what makes a diffirence bewten npc castign a spell by choice vs having it as random mana free proc?

whats recast deay -1?
whats mana cost -1?
mana cost -2?

i see another list which has "attack_proc" and "proc_chance"
but not sure how they apply to ENTIRE list of spells of a given npc?

attack_proc values do not make any sence at all

thanks =)