You are looking at a material called friend

This material allows players to keep a list of friends, enemies, and arch-enemies

Reactions:

wakes - if waking object is set as enemy or kos then show the appropriate warning.

sleeps - if sleeping object is set as enemy or kos then show the appropriate warning.

arrives - if arriving object is set as kos then attack it

Customizing your attack
if you want to, you can script yourself with a whyattack block, where you can say something and set a delay (in seconds) before you automatically attack someone you set as kos.

Example:

##whyattack:
print "[$actor] glares at [$init_obj] and says, 'You have angered me too many times, prepare to die!'";
$attackdelay = 10;

note: in the above code double quotes appear as " so you will have to adjust your code as needed.

Also think what would happen if I called roam within my whyattack block?...

Related:

read the command called setfriend
Code